Commit Graph

42 Commits

Author SHA1 Message Date
Peter Xu 6ca206204f iothread: document about why we need explicit aio_poll()
After consulting Paolo I know why we'd better keep the explicit
aio_poll() in iothread_run().  Document it directly into the code so
that future readers will know the answer from day one.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20190306115532.23025-6-peterx@redhat.com
Message-Id: <20190306115532.23025-6-peterx@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-03-08 10:20:57 +00:00
Peter Xu b60ec76a13 iothread: push gcontext earlier in the thread_fn
We were pushing the context until right before running the gmainloop.
Now since we have everything unconditionally, we can move this
earlier.

One benefit is that now it's done even before init_done_sem, so as
long as the iothread user calls iothread_create() and completes, we
know that the thread stack is ready.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-id: 20190306115532.23025-5-peterx@redhat.com
Message-Id: <20190306115532.23025-5-peterx@redhat.com>

[Tweaked comment wording as discussed with Peter Xu.
--Stefan]

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-03-08 10:20:23 +00:00
Peter Xu 0bd2d233c6 iothread: create main loop unconditionally
Since we've have the gcontext always there, create the main loop
altogether.  The iothread_run() is even cleaner.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-id: 20190306115532.23025-4-peterx@redhat.com
Message-Id: <20190306115532.23025-4-peterx@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-03-08 10:16:15 +00:00
Peter Xu b506e0f16c iothread: create the gcontext unconditionally
In existing code we create the gcontext dynamically at the first
access of the gcontext from caller.  That can bring some complexity
and potential races during using iothread.  Since the context itself
is not that big a resource, and we won't have millions of iothread,
let's simply create the gcontext unconditionally.

This will also be a preparation work further to move the thread
context push operation earlier than before (now it's only pushed right
before we want to start running the gmainloop).

Removing the g_once since it's not necessary, while introducing a new
run_gcontext boolean to show whether we want to run the gcontext.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-id: 20190306115532.23025-3-peterx@redhat.com
Message-Id: <20190306115532.23025-3-peterx@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-03-08 10:16:15 +00:00
Peter Xu 21c4d15b47 iothread: replace init_done_cond with a semaphore
Only sending an init-done message using lock+cond seems an overkill to
me.  Replacing it with a simpler semaphore.

Meanwhile, init the semaphore unconditionally, then we can destroy it
unconditionally too in finalize which seems cleaner.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-id: 20190306115532.23025-2-peterx@redhat.com
Message-Id: <20190306115532.23025-2-peterx@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-03-08 10:16:15 +00:00
Peter Xu 6c95363d97 iothread: fix iothread hang when stop too soon
Lukas reported an hard to reproduce QMP iothread hang on s390 that
QEMU might hang at pthread_join() of the QMP monitor iothread before
quitting:

  Thread 1
  #0  0x000003ffad10932c in pthread_join
  #1  0x0000000109e95750 in qemu_thread_join
      at /home/thuth/devel/qemu/util/qemu-thread-posix.c:570
  #2  0x0000000109c95a1c in iothread_stop
  #3  0x0000000109bb0874 in monitor_cleanup
  #4  0x0000000109b55042 in main

While the iothread is still in the main loop:

  Thread 4
  #0  0x000003ffad0010e4 in ??
  #1  0x000003ffad553958 in g_main_context_iterate.isra.19
  #2  0x000003ffad553d90 in g_main_loop_run
  #3  0x0000000109c9585a in iothread_run
      at /home/thuth/devel/qemu/iothread.c:74
  #4  0x0000000109e94752 in qemu_thread_start
      at /home/thuth/devel/qemu/util/qemu-thread-posix.c:502
  #5  0x000003ffad10825a in start_thread
  #6  0x000003ffad00dcf2 in thread_start

IMHO it's because there's a race between the main thread and iothread
when stopping the thread in following sequence:

    main thread                       iothread
    ===========                       ==============
                                      aio_poll()
    iothread_get_g_main_context
      set iothread->worker_context
    iothread_stop
      schedule iothread_stop_bh
                                        execute iothread_stop_bh [1]
                                          set iothread->running=false
                                          (since main_loop==NULL so
                                           skip to quit main loop.
                                           Note: although main_loop is
                                           NULL but worker_context is
                                           not!)
                                      atomic_read(&iothread->worker_context) [2]
                                        create main_loop object
                                        g_main_loop_run() [3]
    pthread_join() [4]

We can see that when execute iothread_stop_bh() at [1] it's possible
that main_loop is still NULL because it's only created until the first
check of the worker_context later at [2].  Then the iothread will hang
in the main loop [3] and it'll starve the main thread too [4].

Here the simple solution should be that we check again the "running"
variable before check against worker_context.

CC: Thomas Huth <thuth@redhat.com>
CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Lukáš Doktor <ldoktor@redhat.com>
CC: Markus Armbruster <armbru@redhat.com>
CC: Eric Blake <eblake@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-id: 20190129051432.22023-1-peterx@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-02-12 11:49:17 +08:00
Marc-André Lureau 14a2d11825 iothread: fix crash with invalid properties
-object iothread,id=foo,? will crash qemu:

qemu-system-x86_64:qemu-thread-posix.c:128: qemu_cond_destroy: Assertion `cond->initialized' failed.

Use thread_id != -1 to check if iothread_complete() finished
successfully and the mutex/cond have been initialized.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180821100716.13803-1-marcandre.lureau@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
2018-10-12 09:46:14 +08:00
Peter Xu 1554434927 iothread: workaround glib bug which hangs qmp-test
Free the AIO context earlier than the GMainContext (if we have) to
workaround a glib2 bug that GSource context pointer is not cleared even
if the context has already been destroyed (while it should).

The patch itself only changed the order to destroy the objects, no
functional change at all. Without this workaround, we can encounter
qmp-test hang with oob (and possibly any other use case when iothread is
used with GMainContexts):

  #0  0x00007f35ffe45334 in __lll_lock_wait () from /lib64/libpthread.so.0
  #1  0x00007f35ffe405d8 in _L_lock_854 () from /lib64/libpthread.so.0
  #2  0x00007f35ffe404a7 in pthread_mutex_lock () from /lib64/libpthread.so.0
  #3  0x00007f35fc5b9c9d in g_source_unref_internal (source=0x24f0600, context=0x7f35f0000960, have_lock=0) at gmain.c:1685
  #4  0x0000000000aa6672 in aio_context_unref (ctx=0x24f0600) at /root/qemu/util/async.c:497
  #5  0x000000000065851c in iothread_instance_finalize (obj=0x24f0380) at /root/qemu/iothread.c:129
  #6  0x0000000000962d79 in object_deinit (obj=0x24f0380, type=0x242e960) at /root/qemu/qom/object.c:462
  #7  0x0000000000962e0d in object_finalize (data=0x24f0380) at /root/qemu/qom/object.c:476
  #8  0x0000000000964146 in object_unref (obj=0x24f0380) at /root/qemu/qom/object.c:924
  #9  0x0000000000965880 in object_finalize_child_property (obj=0x24ec640, name=0x24efca0 "mon_iothread", opaque=0x24f0380) at /root/qemu/qom/object.c:1436
  #10 0x0000000000962c33 in object_property_del_child (obj=0x24ec640, child=0x24f0380, errp=0x0) at /root/qemu/qom/object.c:436
  #11 0x0000000000962d26 in object_unparent (obj=0x24f0380) at /root/qemu/qom/object.c:455
  #12 0x0000000000658f00 in iothread_destroy (iothread=0x24f0380) at /root/qemu/iothread.c:365
  #13 0x00000000004c67a8 in monitor_cleanup () at /root/qemu/monitor.c:4663
  #14 0x0000000000669e27 in main (argc=16, argv=0x7ffc8b1ae2f8, envp=0x7ffc8b1ae380) at /root/qemu/vl.c:4749

The glib2 bug is fixed in commit 26056558b ("gmain: allow
g_source_get_context() on destroyed sources", 2012-07-30), so the first
good version is glib2 2.33.10. But we still support building with
glib as old as 2.28, so we need the workaround.

Let's make sure we destroy the GSources first before its owner context
until we drop support for glib older than 2.33.10.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180409083956.1780-1-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
2018-04-10 07:43:52 -05:00
Peter Xu 90c558beca iothread: fix breakage on windows
OOB can enable iothread for parsing even on Windows.  We need some tunes
to enable that on Windows otherwise it'll break Windows users.  This
patch fixes the breakage on Windows with qemu-system-ppc.exe.

Reported-by: Howard Spoelstra <hsp.cat7@gmail.com>
Tested-by: Howard Spoelstra <hsp.cat7@gmail.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180322085630.23654-1-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-03-26 14:37:15 +02:00
Stefan Hajnoczi 4486e89c21 vl: introduce vm_shutdown()
Commit 00d09fdbba ("vl: pause vcpus before
stopping iothreads") and commit dce8921b2b
("iothread: Stop threads before main() quits") tried to work around the
fact that emulation was still active during termination by stopping
iothreads.  They suffer from race conditions:
1. virtio_scsi_handle_cmd_vq() racing with iothread_stop_all() hits the
   virtio_scsi_ctx_check() assertion failure because the BDS AioContext
   has been modified by iothread_stop_all().
2. Guest vq kick racing with main loop termination leaves a readable
   ioeventfd that is handled by the next aio_poll() when external
   clients are enabled again, resulting in unwanted emulation activity.

This patch obsoletes those commits by fully disabling emulation activity
when vcpus are stopped.

Use the new vm_shutdown() function instead of pause_all_vcpus() so that
vm change state handlers are invoked too.  Virtio devices will now stop
their ioeventfds, preventing further emulation activity after vm_stop().

Note that vm_stop(RUN_STATE_SHUTDOWN) cannot be used because it emits a
QMP STOP event that may affect existing clients.

It is no longer necessary to call replay_disable_events() directly since
vm_shutdown() does so already.

Drop iothread_stop_all() since it is no longer used.

Cc: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20180307144205.20619-5-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2018-03-08 17:38:51 +00:00
Markus Armbruster 112ed241f5 qapi: Empty out qapi-schema.json
The previous commit improved compile time by including less of the
generated QAPI headers.  This is impossible for stuff defined directly
in qapi-schema.json, because that ends up in headers that that pull in
everything.

Move everything but include directives from qapi-schema.json to new
sub-module qapi/misc.json, then include just the "misc" shard where
possible.

It's possible everywhere, except:

* monitor.c needs qmp-command.h to get qmp_init_marshal()

* monitor.c, ui/vnc.c and the generated qapi-event-FOO.c need
  qapi-event.h to get enum QAPIEvent

Perhaps we'll get rid of those some other day.

Adding a type to qapi/migration.json now recompiles some 120 instead
of 2300 out of 5100 objects.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180211093607.27351-25-armbru@redhat.com>
[eblake: rebase to master]
Signed-off-by: Eric Blake <eblake@redhat.com>
2018-03-02 13:45:50 -06:00
Markus Armbruster e688df6bc4 Include qapi/error.h exactly where needed
This cleanup makes the number of objects depending on qapi/error.h
drop from 1910 (out of 4743) to 1612 in my "build everything" tree.

While there, separate #include from file comment with a blank line,
and drop a useless comment on why qemu/osdep.h is included first.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180201111846.21846-5-armbru@redhat.com>
[Semantic conflict with commit 34e304e975 resolved, OSX breakage fixed]
2018-02-09 13:50:17 +01:00
Stefan Hajnoczi 2362a28ea1 iothread: fix iothread_stop() race condition
There is a small chance that iothread_stop() hangs as follows:

  Thread 3 (Thread 0x7f63eba5f700 (LWP 16105)):
  #0  0x00007f64012c09b6 in ppoll () at /lib64/libc.so.6
  #1  0x000055959992eac9 in ppoll (__ss=0x0, __timeout=0x0, __nfds=<optimized out>, __fds=<optimized out>) at /usr/include/bits/poll2.h:77
  #2  0x000055959992eac9 in qemu_poll_ns (fds=<optimized out>, nfds=<optimized out>, timeout=<optimized out>) at util/qemu-timer.c:322
  #3  0x0000559599930711 in aio_poll (ctx=0x55959bdb83c0, blocking=blocking@entry=true) at util/aio-posix.c:629
  #4  0x00005595996806fe in iothread_run (opaque=0x55959bd78400) at iothread.c:59
  #5  0x00007f640159f609 in start_thread () at /lib64/libpthread.so.0
  #6  0x00007f64012cce6f in clone () at /lib64/libc.so.6

  Thread 1 (Thread 0x7f640b45b280 (LWP 16103)):
  #0  0x00007f64015a0b6d in pthread_join () at /lib64/libpthread.so.0
  #1  0x00005595999332ef in qemu_thread_join (thread=<optimized out>) at util/qemu-thread-posix.c:547
  #2  0x00005595996808ae in iothread_stop (iothread=<optimized out>) at iothread.c:91
  #3  0x000055959968094d in iothread_stop_iter (object=<optimized out>, opaque=<optimized out>) at iothread.c:102
  #4  0x0000559599857d97 in do_object_child_foreach (obj=obj@entry=0x55959bdb8100, fn=fn@entry=0x559599680930 <iothread_stop_iter>, opaque=opaque@entry=0x0, recurse=recurse@entry=false) at qom/object.c:852
  #5  0x0000559599859477 in object_child_foreach (obj=obj@entry=0x55959bdb8100, fn=fn@entry=0x559599680930 <iothread_stop_iter>, opaque=opaque@entry=0x0) at qom/object.c:867
  #6  0x0000559599680a6e in iothread_stop_all () at iothread.c:341
  #7  0x000055959955b1d5 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4913

The relevant code from iothread_run() is:

  while (!atomic_read(&iothread->stopping)) {
      aio_poll(iothread->ctx, true);

and iothread_stop():

  iothread->stopping = true;
  aio_notify(iothread->ctx);
  ...
  qemu_thread_join(&iothread->thread);

The following scenario can occur:

1. IOThread:
  while (!atomic_read(&iothread->stopping)) -> stopping=false

2. Main loop:
  iothread->stopping = true;
  aio_notify(iothread->ctx);

3. IOThread:
  aio_poll(iothread->ctx, true); -> hang

The bug is explained by the AioContext->notify_me doc comments:

  "If this field is 0, everything (file descriptors, bottom halves,
  timers) will be re-evaluated before the next blocking poll(), thus the
  event_notifier_set call can be skipped."

The problem is that "everything" does not include checking
iothread->stopping.  This means iothread_run() will block in aio_poll()
if aio_notify() was called just before aio_poll().

This patch fixes the hang by replacing aio_notify() with
aio_bh_schedule_oneshot().  This makes aio_poll() or g_main_loop_run()
to return.

Implementing this properly required a new bool running flag.  The new
flag prevents races that are tricky if we try to use iothread->stopping.
Now iothread->stopping is purely for iothread_stop() and
iothread->running is purely for the iothread_run() thread.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20171207201320.19284-6-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-12-19 10:25:09 +00:00
Stefan Hajnoczi fbcc6923b0 iothread: add iothread_by_id() API
Encapsulate IOThread QOM object lookup so that callers don't need to
know how and where IOThread objects live.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20171206144550.22295-8-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-12-19 10:25:09 +00:00
Peter Xu 5b3ac23fee iothread: delay the context release to finalize
When gcontext is used with iothread, the context will be destroyed
during iothread_stop().  That's not good since sometimes we would like
to keep the resources until iothread is destroyed, but we may want to
stop the thread before that point.

Delay the destruction of gcontext to iothread finalize.  Then we can do:

  iothread_stop(thread);
  some_cleanup_on_resources();
  iothread_destroy(thread);

We may need this patch if we want to run chardev IOs in iothreads and
hopefully clean them up correctly.  For more specific information,
please see 2b316774f6 ("qemu-char: do not operate on sources from
finalize callbacks").

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-id: 20170928025958.1420-5-peterx@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-10-03 14:36:19 -04:00
Peter Xu 82d90705fe iothread: export iothread_stop()
So that internal iothread users can explicitly stop one iothread without
destroying it.

Since at it, fix iothread_stop() to allow it to be called multiple
times.  Before this patch we may call iothread_stop() more than once on
single iothread, while that may not be correct since qemu_thread_join()
is not allowed to run twice.  From manual of pthread_join():

  Joining with a thread that has previously been joined results in
  undefined behavior.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-id: 20170928025958.1420-4-peterx@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-10-03 14:36:16 -04:00
Peter Xu 0173e21b61 iothread: provide helpers for internal use
IOThread is a general framework that contains IO loop environment and a
real thread behind.  It's also good to be used internally inside qemu.
Provide some helpers for it to create iothreads to be used internally.

Put all the internal used iothreads into the internal object container.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-id: 20170928025958.1420-3-peterx@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-10-03 14:26:15 -04:00
Eduardo Habkost 65072c157e iothread: Make iothread_stop() idempotent
Currently, iothread_stop_all() makes all iothread objects unsafe
to be destroyed, because qemu_thread_join() ends up being called
twice.

To fix this, make iothread_stop() idempotent by checking
thread->stopped.

Fixes the following crash:

  qemu-system-x86_64 -object iothread,id=iothread0 -monitor stdio -display none
  QEMU 2.10.50 monitor - type 'help' for more information
  (qemu) quit
  qemu: qemu_thread_join: No such process
  Aborted (core dumped)

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170926130028.12471-1-ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2017-09-29 10:56:56 +02:00
Wang Yong 329163cbe6 qemu-iothread: IOThread supports the GMainContext event loop
IOThread uses AioContext event loop and does not run a GMainContext.
Therefore,chardev cannot work in IOThread,such as the chardev is
used for colo-compare packets reception.

This patch makes the IOThread run the GMainContext event loop,
chardev and IOThread can work together.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Wang Yong <wang.yong155@zte.com.cn>
Signed-off-by: Wang Guang <wang.guang55@zte.com.cn>
Signed-off-by: Jason Wang <jasowang@redhat.com>
2017-09-08 09:32:48 +08:00
Pavel Hrdina 5fc00480ab monitor: add poll-* properties into query-iothreads result
IOthreads were recently extended by new properties that can
enable/disable and configure aio polling.  This will also allow
other tools that uses QEMU to probe for existence of those new
properties via query-qmp-schema.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Message-Id: <3163c16d6ab4257f7be9ad44fe9cc0ce8c359e5a.1486718555.git.phrdina@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
2017-02-21 18:29:01 +00:00
Stefan Hajnoczi cdd7abfdba iothread: enable AioContext polling by default
IOThread AioContexts are likely to consist only of event sources like
virtqueue ioeventfds and LinuxAIO completion eventfds that are pollable
from userspace (without system calls).

We recently merged the AioContext polling feature but didn't enable it
by default yet.  I have gone back over the performance data on the
mailing list and picked a default polling value that gave good results.

Let's enable AioContext polling by default so users don't have another
switch they need to set manually.  If performance regressions are found
we can still disable this for the QEMU 2.9 release.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Karl Rister <krister@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170126170119.27876-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-02-03 14:23:38 +00:00
Stefan Hajnoczi 5e5db49953 iothread: add poll-grow and poll-shrink parameters
These parameters control the poll time self-tuning algorithm.  They are
optional and will default to sane values if omitted.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20161201192652.9509-14-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-01-03 16:38:50 +00:00
Stefan Hajnoczi 82a4118694 aio: self-tune polling time
This patch is based on the algorithm for the kvm.ko halt_poll_ns
parameter in Linux.  The initial polling time is zero.

If the event loop is woken up within the maximum polling time it means
polling could be effective, so grow polling time.

If the event loop is woken up beyond the maximum polling time it means
polling is not effective, so shrink polling time.

If the event loop makes progress within the current polling time then
the sweet spot has been reached.

This algorithm adjusts the polling time so it can adapt to variations in
workloads.  The goal is to reach the sweet spot while also recognizing
when polling would hurt more than help.

Two new trace events, poll_grow and poll_shrink, are added for observing
polling time adjustment.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20161201192652.9509-13-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-01-03 16:38:50 +00:00
Stefan Hajnoczi 0d9d86fb4d iothread: add polling parameters
Poll mode can be configured with -object iothread,poll-max-ns=NUM.
Polling is disabled with a value of 0 nanoseconds.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20161201192652.9509-7-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-01-03 16:38:49 +00:00
Paolo Bonzini 65c1b5b622 iothread: release AioContext around aio_poll
This is the first step towards having fine-grained critical sections in
dataplane threads, which will resolve lock ordering problems between
address_space_* functions (which need the BQL when doing MMIO, even
after we complete RCU-based dispatch) and the AioContext.

Because AioContext does not use contention callbacks anymore, the
unit test has to be changed.

Previously applied as a0710f7995 and
then reverted.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1477565348-5458-19-git-send-email-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
2016-10-28 21:50:18 +08:00
Paolo Bonzini d16341fa69 iothread: detach all block devices before stopping them
Soon bdrv_drain will not call aio_poll itself on iothreads.  If block
devices are left hanging off the iothread's AioContext, there will be no
one to do I/O for those poor devices.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-Id: <1477565348-5458-13-git-send-email-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
2016-10-28 21:50:18 +08:00
Paolo Bonzini e437016511 aio: introduce qemu_get_current_aio_context
This will be used by BDRV_POLL_WHILE (and thus by bdrv_drain)
to choose how to wait for I/O completion.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1477565348-5458-12-git-send-email-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
2016-10-28 21:50:18 +08:00
Lin Ma eb7b5c3511 iothread: check iothread->ctx before aio_context_unref to avoid assertion
if iothread->ctx is set to NULL, aio_context_unref triggers the assertion:
g_source_unref: assertion 'source != NULL' failed.
The patch fixes it.

Signed-off-by: Lin Ma <lma@suse.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20160926052958.10716-1-lma@suse.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2016-09-28 11:21:46 +01:00
Fam Zheng dce8921b2b iothread: Stop threads before main() quits
Right after main_loop ends, we release various things but keep iothread
alive. The latter is not prepared to the sudden change of resources.

Specifically, after bdrv_close_all(), virtio-scsi dataplane get a
surprise at the empty BlockBackend:

(gdb) bt
    at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:543
    at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:577

It is because the d->conf.blk->root is set to NULL, then
blk_get_aio_context() returns qemu_aio_context, whereas s->ctx is still
pointing to the iothread:

    hw/scsi/virtio-scsi.c:543:

    if (s->dataplane_started) {
        assert(blk_get_aio_context(d->conf.blk) == s->ctx);
    }

To fix this, let's stop iothreads before doing bdrv_close_all().

Cc: qemu-stable@nongnu.org
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1473326931-9699-1-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2016-09-13 11:00:57 +01:00
Peter Maydell d38ea87ac5 all: Clean up includes
Clean up includes so that osdep.h is included first and headers
which it implies are not included manually.

This commit was created with scripts/clean-includes.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1454089805-5470-16-git-send-email-peter.maydell@linaro.org
2016-02-04 17:41:30 +00:00
Paolo Bonzini d21e8776f6 iothread: include id in thread name
This makes it easier to find the desired thread.  Use "IO" plus the id;
even with the 14 character limit on the thread name, enough of the id should
be readable (e.g. "IO iothreadNNN" with three characters for the number).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-id: 1448372804-5034-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2015-12-03 11:08:01 +08:00
Paolo Bonzini ab28bd2312 rcu: actually register threads that have RCU read-side critical sections
Otherwise, grace periods are detected too early!

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-07-24 13:57:45 +02:00
Daniel P. Berrange bc2256c4ae qom: Add helper function for getting user objects root
Add object_get_objects_root() function which is a convenience for
obtaining the Object * located at /objects in the object
composition tree. Convert existing code over to use the new
API where appropriate.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
2015-06-19 18:40:00 +02:00
Stefan Hajnoczi da5e1de95b Revert "iothread: release iothread around aio_poll"
This reverts commit a0710f7995.

In qemu-devel email message <556DBF87.2020908@de.ibm.com>, Christian
Borntraeger writes:

  Having many guests all with a kernel/ramdisk (via -kernel) and
  several null block devices will result in hangs. All hanging
  guests are in partition detection code waiting for an I/O to return
  so very early maybe even the first I/O.

  Reverting that commit "fixes" the hangs.

Reverting this commit for the 2.4 release.  More time is needed to
investigate and correct this patch.

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2015-06-12 13:58:33 +01:00
Thomas Huth ac9541579e Remove various unused functions
The functions tpm_backend_thread_tpm_reset() and iothread_find()
are completely unused, let's remove them.

Signed-off-by: Thomas Huth <huth@tuxfamily.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
2015-05-08 14:11:10 +03:00
Paolo Bonzini a0710f7995 iothread: release iothread around aio_poll
This is the first step towards having fine-grained critical sections in
dataplane threads, which resolves lock ordering problems between
address_space_* functions (which need the BQL when doing MMIO, even
after we complete RCU-based dispatch) and the AioContext.

Because AioContext does not use contention callbacks anymore, the
unit test has to be changed.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1424449612-18215-4-git-send-email-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2015-04-28 15:36:08 +02:00
Chrysostomos Nanakos 2f78e491d7 async: aio_context_new(): Handle event_notifier_init failure
On a system with a low limit of open files the initialization
of the event notifier could fail and QEMU exits without printing any
error information to the user.

The problem can be easily reproduced by enforcing a low limit of open
files and start QEMU with enough I/O threads to hit this limit.

The same problem raises, without the creation of I/O threads, while
QEMU initializes the main event loop by enforcing an even lower limit of
open files.

This commit adds an error message on failure:

 # qemu [...] -object iothread,id=iothread0 -object iothread,id=iothread1
 qemu: Failed to initialize event notifier: Too many open files in system

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-09-22 11:39:48 +01:00
Paolo Bonzini acfb23ad3d AioContext: do not rely on aio_poll(ctx, true) result to end a loop
Currently, whenever aio_poll(ctx, true) has completed all pending
work it returns true *and* the next call to aio_poll(ctx, true)
will not block.

This invariant has its roots in qemu_aio_flush()'s implementation
as "while (qemu_aio_wait()) {}".  However, qemu_aio_flush() does
not exist anymore and bdrv_drain_all() is implemented differently;
and this invariant is complicated to maintain and subtly different
from the return value of GMainLoop's g_main_context_iteration.

All calls to aio_poll(ctx, true) except one are guarded by a
while() loop checking for a request to be incomplete, or a
BlockDriverState to be idle.  The one remaining call (in
iothread.c) uses this to delay the aio_context_release/acquire
pair until the AioContext is quiescent, however:

- we can do the same just by using non-blocking aio_poll,
  similar to how vl.c invokes main_loop_wait

- it is buggy, because it does not ensure that the AioContext
  is released between an aio_notify and the next time the
  iothread goes to sleep.  This leads to hangs when stopping
  the dataplane thread.

In the end, these semantics are a bad match for the current
users of AioContext.  So modify that one exception in iothread.c,
which also fixes the hangs, as well as the testcase so that
it use the same idiom as the actual QEMU code.

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-07-14 12:03:20 +02:00
Stefan Hajnoczi 8c2664d869 iothread: make IOThread struct definition public
Make the IOThread struct definition public so objects can be embedded in
parent structs.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-04-04 20:48:02 +02:00
Stefan Hajnoczi dc3dd0d2be qmp: add query-iothreads command
The "query-iothreads" command returns a list of information about
iothreads.  See the patch for API documentation.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-13 14:42:24 +01:00
Stefan Hajnoczi 88eb7c29e4 iothread: stash thread ID away
Keep the thread ID around so we can report it via QMP.

There's only one problem: qemu_get_thread_id() (gettid() wrapper on
Linux) must be called from the thread itself.  There is no way to get
the thread ID outside the thread.

This patch uses a condvar to wait for iothread_run() to populate the
thread_id inside the thread.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-13 14:42:24 +01:00
Stefan Hajnoczi be8d853766 iothread: add I/O thread object
This is a stand-in for Michael Roth's QContext.  I expect this to be
replaced once QContext is completed.

The IOThread object is an AioContext event loop thread.  This patch adds
the concept of multiple event loop threads, allowing users to define
them.

When SMP guests run on SMP hosts it makes sense to instantiate multiple
IOThreads.  This spreads event loop processing across multiple cores.
Note that additional patches are required to actually bind a device to
an IOThread.

[Andreas Färber <afaerber@suse.de> pointed out that the embedded parent
object instance should be called "parent_obj" and have a newline
afterwards.  This patch has been changed to reflect this.
-- Stefan]

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-13 14:42:24 +01:00