linux-kernel - Re: [PATCH 00/37] fine-grained locking in binder driver

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Message-ID: <20170717124947.GA19102@kroah.com>
Date:   Mon, 17 Jul 2017 14:49:47 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Todd Kjos <tkjos@...roid.com>
Cc:     devel@...verdev.osuosl.org, arve@...roid.com, maco@...gle.com,
        linux-kernel@...r.kernel.org, tkjos@...gle.com
Subject: Re: [PATCH 00/37] fine-grained locking in binder driver

On Fri, Jun 30, 2017 at 08:04:21AM +0200, Greg KH wrote:
> On Thu, Jun 29, 2017 at 12:01:34PM -0700, Todd Kjos wrote:
> > The binder driver uses a global mutex to serialize access to state in a
> > multi-threaded environment. This global lock has been increasingly
> > problematic as Android devices have scaled to more cores. The problem is
> > not so much contention for the global lock which still remains relatively
> > low, but the priority inversion which occurs regularly when a lower
> > priority thread is preempted while holding the lock and a higher priority
> > thread becomes blocked on it. These cases can be especially painful if the
> > lower priority thread runs in the background on a slow core at a low
> > frequency. This often manifests as missed frames or other glitches.
> > 
> > For several years, a hacky solution has been used in many Android devices
> > which disables preemption for most of the time the global mutex is held.
> > This dramatically decreased the cases of glitches induced by priority
> > inversion and increased the average throughput for binder transactions.
> > 
> > Moving to fine-grained locking in this patchset results is a cleaner
> > and more scalable solution than the preempt disable hack. Priority
> > inversion is decreased significantly.
> 
> Yeah, it is great to see this work done!  I'll review these on Monday,
> sorry, am traveling at the moment...

All now queued up in my trees.

thanks,

greg k-h