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Message-ID: <1469134658.2344.12.camel@j-VirtualBox>
Subject: Re: [RFC] Avoid mutex starvation when optimistic spinning is
 disabled
From: Jason Low <jason.low2@hpe.com>
To: imre.deak@intel.com
Cc: jason.low2@hpe.com, Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
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        Daniel Vetter <daniel.vetter@intel.com>,
        Waiman Long <Waiman.Long@hpe.com>, Davidlohr Bueso <dave@stgolabs.net>
Date: Thu, 21 Jul 2016 13:57:38 -0700
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On Wed, 2016-07-20 at 16:29 +0300, Imre Deak wrote:
> On ti, 2016-07-19 at 21:39 -0700, Jason Low wrote:
> > On Tue, 2016-07-19 at 16:04 -0700, Jason Low wrote:
> > > Hi Imre,
> > > 
> > > Here is a patch which prevents a thread from spending too much "time"
> > > waiting for a mutex in the !CONFIG_MUTEX_SPIN_ON_OWNER case.
> > > 
> > > Would you like to try this out and see if this addresses the mutex
> > > starvation issue you are seeing in your workload when optimistic
> > > spinning is disabled?
> > 
> > Although it looks like it didn't take care of the 'lock stealing' case
> > in the slowpath. Here is the updated fixed version:
> 
> This also got rid of the problem, I only needed to change the ww
> functions accordingly. Also, imo mutex_trylock() needs the same
> handling

Good point. I supposed mutex_trylock() may not be causing starvation
issues, but I agree that it makes sense if mutex_trylock() fails too if
threads are supposed to yield to a waiter. I'll make the update.

Thanks,
Jason