From: Peter Zijlstra <peterz@infradead.org>
To: Jason Low <jason.low2@hpe.com>
Cc: Ingo Molnar <mingo@redhat.com>,
imre.deak@intel.com, linux-kernel@vger.kernel.org,
Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hpe.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Tim Chen <tim.c.chen@linux.intel.com>,
terry.rudd@hpe.com, "Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: [PATCH v2] locking/mutex: Prevent lock starvation when spinning is enabled
Date: Thu, 18 Aug 2016 17:18:43 +0200 [thread overview]
Message-ID: <20160818151843.GA10168@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160818142735.GB10121@twins.programming.kicks-ass.net>
On Thu, Aug 18, 2016 at 04:27:35PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 10, 2016 at 11:44:08AM -0700, Jason Low wrote:
> > @@ -556,8 +604,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
> > * other waiters. We only attempt the xchg if the count is
> > * non-negative in order to avoid unnecessary xchg operations:
> > */
> > - if (atomic_read(&lock->count) >= 0 &&
> > + if ((!need_yield_to_waiter(lock) || wakeups > 1) &&
> > + atomic_read(&lock->count) >= 0 &&
> > (atomic_xchg_acquire(&lock->count, -1) == 1))
> > + if (wakeups > 1)
> > + clear_yield_to_waiter(lock);
> > +
> > break;
> >
> > /*
>
> There's some { } gone missing there...
>
> Also, I think I'll change it to avoid that extra wakeups > 1 condition..
Also, its broken, even if we should not trylock, we should still very
much xchg(-1) to mark the lock as having waiters.
next prev parent reply other threads:[~2016-08-19 0:49 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-10 18:44 [PATCH v2] locking/mutex: Prevent lock starvation when spinning is enabled Jason Low
2016-08-10 20:00 ` kbuild test robot
2016-08-10 20:01 ` kbuild test robot
2016-08-16 20:19 ` Jason Low
2016-08-10 22:07 ` Jason Low
2016-08-11 2:30 ` Jason Low
2016-08-11 15:40 ` Waiman Long
2016-08-16 19:44 ` Jason Low
2016-08-17 1:41 ` Wanpeng Li
2016-08-17 18:30 ` Jason Low
2016-08-18 0:38 ` Wanpeng Li
2016-08-18 14:14 ` Peter Zijlstra
2016-08-18 15:22 ` Waiman Long
2016-08-18 14:27 ` Peter Zijlstra
2016-08-18 15:18 ` Peter Zijlstra [this message]
2016-08-18 15:30 ` Peter Zijlstra
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