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

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Message-ID: <20080227130716.GB1340@wotan.suse.de>
Date:	Wed, 27 Feb 2008 14:07:16 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andi Kleen <ak@...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 Wed, Feb 27, 2008 at 02:04:18PM +0100, Andi Kleen wrote:
> 
> > 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.

*vmalloc* TLB flushing. 

void flush_tlb_all(void)
{
        on_each_cpu(do_flush_tlb_all, NULL, 1, 1);
}

Of course we could use a new vector for it and speed it up a lot more,
but after my vmalloc improvements I think that would be a waste of a
vector at this point.

 
> > 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.

Oh really? Coming from what callers?
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