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

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Message-Id: <200808282259.43550.denys@visp.net.lb>
Date:	Thu, 28 Aug 2008 22:59:43 +0300
From:	Denys Fedoryshchenko <denys@...p.net.lb>
To:	David Miller <davem@...emloft.net>
Cc:	andi@...stfloor.org, jmalicki@...acarta.com, johnpol@....mipt.ru,
	dada1@...mosbay.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, juhlenko@...mai.com, sammy@...my.net
Subject: Re: loaded router, excessive getnstimeofday in oprofile

On Thursday 28 August 2008, David Miller wrote:
> From: Denys Fedoryshchenko <denys@...p.net.lb>
> Date: Thu, 28 Aug 2008 19:48:52 +0300
>
> > So there is few good solutions available (IMHO):
> > 1)Introduce some SO_REALTIMESTAMP (anyway even SO_TIMESTAMP not defined
> > in any standard) for banks and ntp folks, who need them. And even give
> > them timespec instead timeval, so they will be even more happy with
> > resolution. 2)Provide sysctl,kernel boot, or even "build time" option for
> > "banks" to have high resolution(and expensive) SO_TIMESTAMP.
>
> The performance hit hurts, but changing the default to lower
> resolution after it having been high resolution for 10+ years
> is a regression and something we really can't do.
Agree. Then maybe to add way to choose, because choice is high resolution vs 
performance. For example Intel dynamically throttling interrupts on e1000*, 
and it saves me in this case. They leave also option for users who wants low 
latency/high troughput.
So maybe there must be a way for specific functions who uses get(ns)timeofday  
to use specific timers (cheap and less precise), by option. Or to limit 
amount of calls to timer by them.
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