linux-kernel - Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock

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Message-ID: <1437010465.28475.1.camel@ellerman.id.au>
Date:	Thu, 16 Jul 2015 11:34:25 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Will Deacon <will.deacon@....com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH v2] memory-barriers: remove
 smp_mb__after_unlock_lock()

On Wed, 2015-07-15 at 07:18 -0700, Paul E. McKenney wrote:
> On Wed, Jul 15, 2015 at 01:06:18PM +1000, Michael Ellerman wrote:
> > On Tue, 2015-07-14 at 08:31 +1000, Benjamin Herrenschmidt wrote:
> > > Michael, at some point you were experimenting a bit with that and tried
> > > to get some perf numbers of the impact that would have, did that
> > > solidify ? Otherwise, I'll have a look when I'm back next week.
> > 
> > I was mainly experimenting with replacing the lwsync in lock with an isync.
> > 
> > But I think you're talking about making it a full sync in lock.
> > 
> > That was about +7% on p8, +25% on p7 and +88% on p6.
> 
> Just for completeness, what were you running as benchmark?  ;-)

Heh sorry :)

That was my lockcomparison benchmark, based on Anton's original. It just does
100,000,000 lock/unlocks for each type in userspace:

  https://github.com/mpe/lockcomparison/blob/master/lock_comparison.c

cheers


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