From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49524) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1d3kv6-0007Dk-GV for qemu-devel@nongnu.org; Thu, 27 Apr 2017 11:01:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1d3kv2-0004KN-LI for qemu-devel@nongnu.org; Thu, 27 Apr 2017 11:01:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46338) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1d3kv2-0004JR-Bb for qemu-devel@nongnu.org; Thu, 27 Apr 2017 11:01:20 -0400 Date: Thu, 27 Apr 2017 11:01:05 -0400 (EDT) From: Paolo Bonzini Message-ID: <1979006830.1310182.1493305265379.JavaMail.zimbra@redhat.com> In-Reply-To: <20170427145926.GA32606@pacoca> References: <1493054398-26013-1-git-send-email-joserz@linux.vnet.ibm.com> <20170427145926.GA32606@pacoca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2] trace: add qemu mutex lock and unlock trace events List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: joserz@linux.vnet.ibm.com Cc: famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com ----- Original Message ----- > From: joserz@linux.vnet.ibm.com > To: "Paolo Bonzini" > Cc: famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com > Sent: Thursday, April 27, 2017 4:59:26 PM > Subject: Re: [Qemu-devel] [PATCH v2] trace: add qemu mutex lock and unlock trace events > > On Thu, Apr 27, 2017 at 10:55:04AM +0200, Paolo Bonzini wrote: > > > > > > On 24/04/2017 19:19, Jose Ricardo Ziviani wrote: > > > These trace events were very useful to help me to understand and find a > > > reordering issue in vfio, for example: > > > > > > qemu_mutex_lock locked mutex 0x10905ad8 > > > vfio_region_write (0001:03:00.0:region1+0xc0, 0x2020c, 4) > > > qemu_mutex_unlock unlocked mutex 0x10905ad8 > > > qemu_mutex_lock locked mutex 0x10905ad8 > > > vfio_region_write (0001:03:00.0:region1+0xc4, 0xa0000, 4) > > > qemu_mutex_unlock unlocked mutex 0x10905ad8 > > > > > > that also helped me to see the desired result after the fix: > > > > > > qemu_mutex_lock locked mutex 0x10905ad8 > > > vfio_region_write (0001:03:00.0:region1+0xc0, 0x2000c, 4) > > > vfio_region_write (0001:03:00.0:region1+0xc4, 0xb0000, 4) > > > qemu_mutex_unlock unlocked mutex 0x10905ad8 > > > > > > So it could be a good idea to have these traces implemented. It's worth > > > mentioning that they should be surgically enabled during the debugging, > > > otherwise it can flood the trace logs with lock/unlock messages. > > > > > > How to use it: > > > trace-event qemu_mutex_lock on|off > > > trace-event qemu_mutex_unlock on|off > > > or > > > trace-event qemu_mutex* on|off > > > > > > Signed-off-by: Jose Ricardo Ziviani > > > > Some improvements: > > > > 1) handle trylock and Win32 too > > > > 2) pass mutex instead of &mutex->lock, it is the same but the latter is > > unnecessarily obfuscated > > > > 3) also trace unlock/lock around cond_wait > > > > 4) trace "unlocked" before calling pthread_mutex_unlock, so that it is > > always placed before the next "locked" tracepoint. > > I'm working on it > Thanks for your review! No need, if you agree with the change below I can just queue the modified patch. Paolo > > > > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c > > index bf5756763d..46f4c08e6d 100644 > > --- a/util/qemu-thread-posix.c > > +++ b/util/qemu-thread-posix.c > > @@ -62,7 +62,7 @@ void qemu_mutex_lock(QemuMutex *mutex) > > if (err) > > error_exit(err, __func__); > > > > - trace_qemu_mutex_lock(&mutex->lock); > > + trace_qemu_mutex_locked(mutex); > > } > > > > int qemu_mutex_trylock(QemuMutex *mutex) > > @@ -71,7 +71,7 @@ int qemu_mutex_trylock(QemuMutex *mutex) > > > > err = pthread_mutex_trylock(&mutex->lock); > > if (err == 0) { > > - trace_qemu_mutex_lock(&mutex->lock); > > + trace_qemu_mutex_locked(mutex); > > return 0; > > } > > if (err == EBUSY) { > > @@ -84,11 +84,10 @@ void qemu_mutex_unlock(QemuMutex *mutex) > > { > > int err; > > > > + trace_qemu_mutex_unlocked(mutex); > > err = pthread_mutex_unlock(&mutex->lock); > > if (err) > > error_exit(err, __func__); > > - > > - trace_qemu_mutex_unlock(&mutex->lock); > > } > > > > void qemu_rec_mutex_init(QemuRecMutex *mutex) > > @@ -145,7 +144,9 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex) > > { > > int err; > > > > + trace_qemu_mutex_unlocked(mutex); > > err = pthread_cond_wait(&cond->cond, &mutex->lock); > > + trace_qemu_mutex_locked(mutex); > > if (err) > > error_exit(err, __func__); > > } > > diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c > > index d3c87bc89e..0dc3ae7756 100644 > > --- a/util/qemu-thread-win32.c > > +++ b/util/qemu-thread-win32.c > > @@ -55,6 +55,7 @@ void qemu_mutex_destroy(QemuMutex *mutex) > > void qemu_mutex_lock(QemuMutex *mutex) > > { > > AcquireSRWLockExclusive(&mutex->lock); > > + trace_qemu_mutex_locked(mutex); > > } > > > > int qemu_mutex_trylock(QemuMutex *mutex) > > @@ -64,6 +64,7 @@ int qemu_mutex_trylock(QemuMutex *mutex) > > > > owned = TryAcquireSRWLockExclusive(&mutex->lock); > > if (owned) { > > + trace_qemu_mutex_locked(mutex); > > return 0; > > } > > return -EBUSY; > > @@ -72,6 +72,7 @@ int qemu_mutex_trylock(QemuMutex *mutex) > > > > void qemu_mutex_unlock(QemuMutex *mutex) > > { > > + trace_qemu_mutex_unlocked(mutex); > > ReleaseSRWLockExclusive(&mutex->lock); > > } > > > > @@ -124,7 +124,9 @@ void qemu_cond_broadcast(QemuCond *cond) > > > > void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex) > > { > > + trace_qemu_mutex_unlocked(mutex); > > SleepConditionVariableSRW(&cond->var, &mutex->lock, INFINITE, 0); > > + trace_qemu_mutex_locked(mutex); > > } > > > > void qemu_sem_init(QemuSemaphore *sem, int init) > > diff --git a/util/trace-events b/util/trace-events > > index 70f62124e1..fa540c620b 100644 > > --- a/util/trace-events > > +++ b/util/trace-events > > @@ -57,5 +57,5 @@ lockcnt_futex_wait_resume(const void *lockcnt, int > > new) "lockcnt %p after wait: > > lockcnt_futex_wake(const void *lockcnt) "lockcnt %p waking up one waiter" > > > > # util/qemu-thread-posix.c > > -qemu_mutex_lock(void *lock) "locked mutex %p" > > -qemu_mutex_unlock(void *lock) "unlocked mutex %p" > > +qemu_mutex_locked(void *lock) "locked mutex %p" > > +qemu_mutex_unlocked(void *lock) "unlocked mutex %p" > > > > >