linux-kernel - Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64

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Message-ID: <20130702063912.GA3143@gmail.com>
Date:	Tue, 2 Jul 2013 08:39:12 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Wedson Almeida Filho <wedsonaf@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64


* Borislav Petkov <bp@...en8.de> wrote:

> On Mon, Jul 01, 2013 at 03:35:47PM -0700, Wedson Almeida Filho wrote:
> > On Mon, Jul 1, 2013 at 3:28 PM, Borislav Petkov <bp@...en8.de> wrote:
> > >
> > > perf stat --repeat 10 -a --sync --pre 'make -s clean; echo 1 > /proc/sys/vm/drop_caches' make -s -j64 bzImage
> > 
> > How many CPUs do you have in your system? Maybe -j64 vs -jNUM_CPUs
> > affects your measurements as well.
> 
> 8. But that shouldn't matter since I made the non-differing measurements 
> two mails back with -j64.
> 
> Also -j9, i.e. -j$(($NUM_CPUS+1)) gives "121.613217871 seconds time 
> elapsed" because with -j9 the probability of some core not executing a 
> make thread for whatever reason is higher than with -j64. But it is only 
> as high as an additional 1s with this workload.
> 
> I think with -j64 Ingo meant to saturate the scheduler to make sure 
> there always are runnable threads more than cores available so that we 
> can maximize the core utilization with threads running our workload.

Yeah - I didn't know your CPU count, -j64 is what I use.

Also, just in case it wasn't clear: thanks for the measurements - and I'd 
be in favor of merging this patch if it shows any improvement or if 
measurements lie within noise, because per asm review the change should be 
a win.

Thanks,

	Ingo
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