linux-kernel - Re: inlined spinlocks on sparc64

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Date:	Thu, 13 Aug 2009 13:56:23 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, heiko.carstens@...ibm.com
Subject: Re: inlined spinlocks on sparc64

On Thu, Aug 13 2009, David Miller wrote:
> From: Jens Axboe <jens.axboe@...cle.com>
> Date: Thu, 13 Aug 2009 10:20:58 +0200
> 
> > I deleted the original thread, so I can't reply there. Just a heads up
> > on the spinlock inlining on sparc64. I decided to give your patches a
> > shot, since one of my IO benchmarks here basically degenerates into a
> > spinlock microbenchmark with > 50% time spent there (unlock part,
> > according to perf). Some of that is surely caching effects, but still.
> > 
> > For this particular workload, I get a net improvement of about 3.5% with
> > the inlined functions. Not bad.
> 
> Doesn't surprise me, any function call can result in a register
> window spill onto the stack, and that's 128 bytes of writes.
> 
> Later when you leave the code path you have to refill that spilled
> window and you get 128 bytes of reads for each one of those.

Good thing it's not register starved ;-)

Forgot to mention that it grew my kernel image by exactly 80KB, total
size is around 5.5MB.

-- 
Jens Axboe

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