linux-kernel - Re: [rfc][patch] x86-64 new smp_call

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Date:	Wed, 27 Feb 2008 14:04:18 +0100
From:	Andi Kleen <ak@...e.de>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org
Subject: Re: [rfc][patch] x86-64 new smp_call_function design


> On a 2 socket, 8 core system, I see anywhere up to nearly 16x better
> performance on a stress test. The common cases of call-all, and wait
> are improved the least, however I think that if call-single and nowait
> are turned into a high performance API, then new usages will pop up
> (eg. I started this because I wanted to do "call single, nowait" calls
> for migrating block IO completions back to submitting CPU; however I
> am also interested in improving the "call all, wait" case for example
> to improve vmalloc tlb flushing).

TLB flushing at least on x86-64 should be already well optimized on its
own. I would be surprised if you could do much better.

> As far as I understand, calling a subset of online CPUs that is not all or
> one, is used quite infrequently, so this might be OK.

With cpusets and isolation etc. it is the normal case.

-Andi
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