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

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Date:   Fri, 30 Jun 2017 08:04:21 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Todd Kjos <tkjos@...roid.com>
Cc:     arve@...roid.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, maco@...gle.com, tkjos@...gle.com
Subject: Re: [PATCH 00/37] fine-grained locking in binder driver

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...

thanks,

greg k-h