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>
We have had some tracing tools for mutex but it's not easy to use them
for e.g. dead locks. Let's provide "--enable-debug-mutex" parameter
when configure to allow QemuMutex to store the last owner that took
specific lock. It will be easy to use this tool to debug deadlocks
since we can directly know who took the lock then as long as we can have
a debugger attached to the process.
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180425025459.5258-4-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
We never noticed because it has no users.
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1510273811-13419-1-git-send-email-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
In qemu-thread-posix.c we have two implementations of the
various qemu_sem_* functions, one of which uses native POSIX
sem_* and the other of which emulates them with pthread conditions.
This is necessary because not all our host OSes support
sem_timedwait().
Instead of a hard-coded list of OSes which don't implement
sem_timedwait(), which gets out of date, make configure
test for the presence of the function and set a new
CONFIG_HAVE_SEM_TIMEDWAIT appropriately.
In particular, newer NetBSDs have sem_timedwait(), so this
commit will switch them over to using it. OSX still does
not have an implementation.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Kamil Rytarowski <n54@gmx.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Not all platforms check whether a lock is initialized before used. In
particular Linux seems to be more permissive than OSX.
Check initialization state explicitly in our code to catch such bugs
earlier.
Signed-off-by: Fam Zheng <famz@redhat.com>
Message-Id: <20170704122325.25634-1-famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
GRecMutex is new in glib 2.32, so we cannot use it. Introduce
a recursive mutex in qemu-thread instead, which will be used
instead of RFifoLock.
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1477565348-5458-20-git-send-email-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Tracked down with an ugly, brittle and probably buggy Perl script.
Also move includes converted to <...> up so they get included before
ours where that's obviously okay.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Tested-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
This emulates Win32 manual-reset events using futexes or conditional
variables. Typical ways to use them are with multi-producer,
single-consumer data structures, to test for a complex condition whose
elements come from different threads:
for (;;) {
qemu_event_reset(ev);
... test complex condition ...
if (condition is true) {
break;
}
qemu_event_wait(ev);
}
Or more efficiently (but with some duplication):
... evaluate condition ...
while (!condition) {
qemu_event_reset(ev);
... evaluate condition ...
if (!condition) {
qemu_event_wait(ev);
... evaluate condition ...
}
}
QemuEvent provides a very fast userspace path in the common case when
no other thread is waiting, or the event is not changing state.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Fix following bugs in "fallback implementation of counting semaphores
with mutex+condvar" added in c166cb72f1:
- waiting threads are not restarted properly if more than one threads
are waiting unblock signals in qemu_sem_timedwait()
- possible missing pthread_cond_signal(3) calls when waiting threads
are returned by ETIMEDOUT
- fix an uninitialized variable
The problem is analyzed by and fix is provided by Noriyuki Soda.
Also put additional cleanup suggested by Laszlo Ersek:
- make QemuSemaphore.count unsigned (it won't be negative)
- check a return value of in pthread_cond_wait() in qemu_sem_wait()
Signed-off-by: Izumi Tsutsui <tsutsui@ceres.dti.ne.jp>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Message-id: 1372841894-10634-1-git-send-email-tsutsui@ceres.dti.ne.jp
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Disable the semaphores fallback code for OpenBSD as modern OpenBSD
releases now have sem_timedwait().
Signed-off-by: Brad Smith <brad@comstyle.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
