Date: Thu, 16 Nov 2017 23:21:18 -0800 From: Cy Schubert <Cy.Schubert@komquats.com> To: Mateusz Guzik <mjg@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r325920 - head/sys/kern Message-ID: <201711170721.vAH7LIfW004556@slippy.cwsent.com> In-Reply-To: Message from Mateusz Guzik <mjg@FreeBSD.org> of "Fri, 17 Nov 2017 02:25:04 %2B0000." <201711170225.vAH2P4jY046885@repo.freebsd.org>
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In message <201711170225.vAH2P4jY046885@repo.freebsd.org>, Mateusz Guzik writes : > Author: mjg > Date: Fri Nov 17 02:25:04 2017 > New Revision: 325920 > URL: https://svnweb.freebsd.org/changeset/base/325920 > > Log: > mtx: unlock before traversing threads to wake up > > This shortens the lock hold time while not affecting corretness. > All the woken up threads end up competing can lose the race against > a completely unrelated thread getting the lock anyway. > > Modified: > head/sys/kern/kern_mutex.c > > Modified: head/sys/kern/kern_mutex.c > ============================================================================= > = > --- head/sys/kern/kern_mutex.c Fri Nov 17 02:22:51 2017 (r32591 > 9) > +++ head/sys/kern/kern_mutex.c Fri Nov 17 02:25:04 2017 (r32592 > 0) > @@ -629,7 +629,8 @@ __mtx_lock_sleep(volatile uintptr_t *c, uintptr_t v) > #ifdef KDTRACE_HOOKS > sleep_time -= lockstat_nsecs(&m->lock_object); > #endif > - turnstile_wait(ts, mtx_owner(m), TS_EXCLUSIVE_QUEUE); > + MPASS(owner == mtx_owner(m)); Should this be conditional when ADAPTIVE_MUTEXES is defined? Otherwise it fails to build. > + turnstile_wait(ts, owner, TS_EXCLUSIVE_QUEUE); > #ifdef KDTRACE_HOOKS > sleep_time += lockstat_nsecs(&m->lock_object); > sleep_cnt++; > @@ -1002,7 +1003,7 @@ __mtx_unlock_sleep(volatile uintptr_t *c) > { > struct mtx *m; > struct turnstile *ts; > - uintptr_t tid, v; > + uintptr_t tid; > > if (SCHEDULER_STOPPED()) > return; > @@ -1028,12 +1029,12 @@ __mtx_unlock_sleep(volatile uintptr_t *c) > * can be removed from the hash list if it is empty. > */ > turnstile_chain_lock(&m->lock_object); > + _mtx_release_lock_quick(m); > ts = turnstile_lookup(&m->lock_object); > + MPASS(ts != NULL); > if (LOCK_LOG_TEST(&m->lock_object, opts)) > CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m); > - MPASS(ts != NULL); > turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE); > - _mtx_release_lock_quick(m); > > /* > * This turnstile is now no longer associated with the mutex. We can > -- Cheers, Cy Schubert <Cy.Schubert@cschubert.com> FreeBSD UNIX: <cy@FreeBSD.org> Web: http://www.FreeBSD.org The need of the many outweighs the greed of the few.
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