linux-kernel - Re: [PATCH 0 of 8] x86/smp function calls: convert x86 tlb flushes to use function calls

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Date:	Mon, 11 Aug 2008 16:57:26 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	x86@...nel.org, Nick Piggin <nickpiggin@...oo.com.au>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 0 of 8] x86/smp function calls: convert x86 tlb flushes
 to use function calls

Andi Kleen wrote:
> Micro benchmark. Just stick RDTSC around the calls and trigger
> a few remote flushes by e.g. doing mmap/munmap on a multithreaded program
> running on different CPUs.
>   

On a HT 3GHz Xeon, I see a ~35% increase in time (1830ns -> 2500ns), 
averaged over 1000,000 interrupts.  Because it's only 2 cpu, it ends up 
always using the smp_call_function_single path (but via the 
smp_call_function_mask path).

I need to try getting a more-cpu machine running native to do a proper 
test, esp to see if putting kmalloc on that path is very expensive or 
not.  (Is it worth using a kmem_cache?)

    J
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