linux-kernel - Re: loaded router, excessive getnstimeofday in oprofile\

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Message-Id: <20080827.152314.218610441.davem@davemloft.net>
Date:	Wed, 27 Aug 2008 15:23:14 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	andi@...stfloor.org
Cc:	dada1@...mosbay.com, rick.jones2@...com, johnpol@....mipt.ru,
	denys@...p.net.lb, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: loaded router, excessive getnstimeofday in oprofile\

From: Andi Kleen <andi@...stfloor.org>
Date: Wed, 27 Aug 2008 20:32:16 +0200

> > Doing the expensive timestamping in a possibly delayed thread (ie some 
> > milliseconds
> > after hardware notification) is wrong/useless.
> 
> We had this discussion earlier, please review the thread I linked to. 
> 
> Note that interrupts can be arbitarily delayed too (both by cli
> and by interrupt mitigation), even on a non RT kernel.

This is a much different kind of delay compared to sleeping for seconds
or longer on the socket lock while a GFP_KERNEL allocation is being
satisfied by swapping tons of crap out to disk.

Your socket solution is not a workable scheme.
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