Commit Graph

13 Commits

Author SHA1 Message Date
Stefan Hajnoczi d73415a315 qemu/atomic.h: rename atomic_ to qatomic_
clang's C11 atomic_fetch_*() functions only take a C11 atomic type
pointer argument. QEMU uses direct types (int, etc) and this causes a
compiler error when a QEMU code calls these functions in a source file
that also included <stdatomic.h> via a system header file:

  $ CC=clang CXX=clang++ ./configure ... && make
  ../util/async.c:79:17: error: address argument to atomic operation must be a pointer to _Atomic type ('unsigned int *' invalid)

Avoid using atomic_*() names in QEMU's atomic.h since that namespace is
used by <stdatomic.h>. Prefix QEMU's APIs with 'q' so that atomic.h
and <stdatomic.h> can co-exist. I checked /usr/include on my machine and
searched GitHub for existing "qatomic_" users but there seem to be none.

This patch was generated using:

  $ git grep -h -o '\<atomic\(64\)\?_[a-z0-9_]\+' include/qemu/atomic.h | \
    sort -u >/tmp/changed_identifiers
  $ for identifier in $(</tmp/changed_identifiers); do
        sed -i "s%\<$identifier\>%q$identifier%g" \
            $(git grep -I -l "\<$identifier\>")
    done

I manually fixed line-wrap issues and misaligned rST tables.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200923105646.47864-1-stefanha@redhat.com>
2020-09-23 16:07:44 +01:00
Dr. David Alan Gilbert 2a86be2571 qsp: Use WITH_RCU_READ_LOCK_GUARD
The automatic rcu read lock maintenance works quite
nicely in this case where it previously relied on a comment to
delimit the lifetime and now has a block.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2019-12-17 19:33:52 +01:00
Yury Kotov 3dcc9c6ec4 qemu-thread: Add qemu_cond_timedwait
The new function is needed to implement conditional sleep for CPU
throttling. It's possible to reuse qemu_sem_timedwait, but it's more
difficult than just add qemu_cond_timedwait.

Also moved compute_abs_deadline function up the code to reuse it in
qemu_cond_timedwait_impl win32.

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
Message-Id: <20190909131335.16848-2-yury-kotov@yandex-team.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2019-09-16 17:13:06 +02:00
Markus Armbruster ac7ff4cf5f qsp: Simplify how qsp_report() prints
qsp_report() takes an fprintf()-like callback and a FILE * to pass to
it.

Its only caller hmp_sync_profile() passes monitor_fprintf() and the
current monitor cast to FILE *.  monitor_fprintf() casts it right
back, and is otherwise identical to monitor_printf().  The
type-punning is ugly.

Drop the callback, and call qemu_printf() instead.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190417191805.28198-7-armbru@redhat.com>
2019-04-18 22:18:59 +02:00
Emilio G. Cota fe656e3185 include: move exec/tb-hash-xx.h to qemu/xxhash.h
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Emilio G. Cota c971d8fa73 exec: introduce qemu_xxhash{2,4,5,6,7}
Before moving them all to include/qemu/xxhash.h.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-12-17 06:04:44 +03:00
Emilio G. Cota ac8c77486c qsp: use atomic64 accessors
With the seqlock, we either have to use atomics to remain
within defined behaviour (and note that 64-bit atomics aren't
always guaranteed to compile, irrespective of __nocheck), or
drop the atomics and be in undefined behaviour territory.

Fix it by dropping the seqlock and using atomic64 accessors.
This will limit scalability when !CONFIG_ATOMIC64, but those
machines (1) don't have many users and (2) are unlikely to
have many cores.

- With CONFIG_ATOMIC64:
$ tests/atomic_add-bench -n 1 -m -p
 Throughput:         13.00 Mops/s

- Forcing !CONFIG_ATOMIC64:
$ tests/atomic_add-bench -n 1 -m -p
 Throughput:         10.89 Mops/s

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20180910232752.31565-5-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-10-02 18:47:55 +02:00
Emilio G. Cota 78255ba2cc qht: drop ht argument from qht iterators
Accessing the HT from an iterator results almost always
in a deadlock. Given that only one qht-internal function
uses this argument, drop it from the interface.

Suggested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2018-09-26 08:55:54 -07:00
Emilio G. Cota cb764d0665 qsp: track BQL callers explicitly
The BQL is acquired via qemu_mutex_lock_iothread(), which makes
the profiler assign the associated wait time (i.e. most of
BQL wait time) entirely to that function. This loses the original
call site information, which does not help diagnose BQL contention.
Fix it by tracking the callers explicitly.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-08-23 18:46:25 +02:00
Emilio G. Cota d557de4a0e qsp: support call site coalescing
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-08-23 18:46:25 +02:00
Emilio G. Cota 996e8d9a45 qsp: add qsp_reset
I first implemented this by deleting all entries in the global
hash table. But doing that safely slows down profiling, since
we'd need to introduce rcu_read_lock/unlock in the fast path.

What's implemented here avoids messing with the thread-local
data in the global hash table. It achieves this by taking a snapshot
of the current state, so that subsequent reports present the delta
wrt to the snapshot.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-08-23 18:46:25 +02:00
Emilio G. Cota 0a22777c71 qsp: add sort_by option to qsp_report
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-08-23 18:46:25 +02:00
Emilio G. Cota fe9959a275 qsp: QEMU's Synchronization Profiler
The goal of this module is to profile synchronization primitives (i.e.
mutexes, recursive mutexes and condition variables) so that scalability
issues can be quickly diagnosed.

Sync primitives are profiled by QSP based on the vaddr of the object accessed
as well as the call site (file:line_nr). That means the same object called
from two different call sites will be tracked in separate entries, which
might be reported together or separately (see subsequent commit on
call site coalescing).

Some perf numbers:

Host: Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
Command: taskset -c 0 tests/atomic_add-bench -d 5 -m

- Before: 54.80 Mops/s
- After:  54.75 Mops/s

That is, a negligible slowdown due to the now indirect call to
qemu_mutex_lock. Note that using a branch instead of an indirect
call introduces a more severe slowdown (53.65 Mops/s, i.e. 2% slowdown).

Enabling the profiler (with -p, added in this series) is more interesting:

- No profiling: 54.75 Mops/s
- W/ profiling: 12.53 Mops/s

That is, a 4.36X slowdown.

We can break down this slowdown by removing the get_clock calls or
the entry lookup:

- No profiling:     54.75 Mops/s
- W/o get_clock:    25.37 Mops/s
- W/o entry lookup: 19.30 Mops/s
- W/ profiling:     12.53 Mops/s

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-08-23 18:46:25 +02:00