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

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Message-ID: <20080829084318.04f0fad8@extreme>
Date:	Fri, 29 Aug 2008 08:43:18 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Denys Fedoryshchenko <denys@...p.net.lb>
Cc:	Eric Dumazet <dada1@...mosbay.com>,
	Andi Kleen <andi@...stfloor.org>,
	Joe Malicki <jmalicki@...acarta.com>,
	David Miller <davem@...emloft.net>, johnpol@....mipt.ru,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	juhlenko@...mai.com, sammy@...my.net
Subject: Re: loaded router, excessive getnstimeofday in oprofile

On Thu, 28 Aug 2008 22:55:29 +0300
Denys Fedoryshchenko <denys@...p.net.lb> wrote:

> On Thursday 28 August 2008, Eric Dumazet wrote:
> > OK, please try oprofile with call graph analysis.
> I did already. Even because most of programs (except ripd/zebra) can be 
> killed, and i kill them, it doesn't change almost anything.
> 
> it seems heavy things causing instability:
> 
> 1)HTB (resolution can be lowered to improve performance, i will try Jarek 
> patch soon)

If you are doing HTB it also calls clock to get timing information.
Each packet dequeue in htb calls psched_get_time() and that becomes
another call nano-second real time clock.

If your embedded processor has really expensive clock, you probably
just want to provide an alternative cheaper time source with less
resolution.

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