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: <20080819074846.GE9807@one.firstfloor.org>
Date:	Tue, 19 Aug 2008 09:48:46 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <andi@...stfloor.org>, 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]

> 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.

-Andi
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