linux-kernel - Re: [PATCH 0 of 9] x86/smp function calls: convert x86 tlb flushes to use function calls [POST 2]

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Message-ID: <48AA7E8C.8030806@goop.org>
Date:	Tue, 19 Aug 2008 01:04:28 -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 9] x86/smp function calls: convert x86 tlb flushes
 to use function calls [POST 2]

Andi Kleen wrote:
>> Don't pay attention to that number.  It's only the extra latency of a HT
>> context->HT context function call + tlb flush.  Which means 1) the tlb
>> is shared anyway, so the extra flush is redundant, 2) they're not really
>> concurrent, 3) it's going down the single-cpu call, rather than the
>> multi-cpu one, 4) it's only measuring the latency for a particular tlb
>> flush, and doesn't take into account any throughput improvements the
>> extra queueing may add.
>>     
>
> A lot of flushes are synchronous. See the rest of my email that
> you snipped.

Yep, sure, but I just wanted to be clear that the 35% number is almost
useless in isolation, and the first step is to do proper measurements.

    J
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