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

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Date:	Tue, 26 Aug 2008 09:51:26 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Denys Fedoryshchenko <denys@...p.net.lb>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: loaded router, excessive getnstimeofday in oprofile

On 22-08-2008 03:57, Denys Fedoryshchenko wrote:
> I have loaded router (~650 Mbps In+Out), based on 2xAMD Opteron 248, Sun Fire 
> X4100. HPET timer available (TSC seems not available on this platform).
> Network interfaces is onboard, connected over PCI-X.
> 
> Right now i am using only one processor, cause using only one interface and 
> interrupts stick to it. Other is almost not used.
> At peak time i notice in mpstat, that this processor is almost "dead", and if 
> i run minor application consuming resources - ping over this router will be 
> terrible. For me it is clear - system overloaded. I did oprofile, and here is 
> result (at low load time, but at peak time it is very similar).
...
> CPU: AMD64 processors, speed 2193.74 MHz (estimated)
> Counted CPU_CLK_UNHALTED events (Cycles outside of halt state) with a unit 
> mask of 0x00 (No unit mask) count 100000
> samples  %        symbol name
> 1031727  37.1736  getnstimeofday
> 230457    8.3035  __napi_schedule
> 122154    4.4013  __do_softirq
> 110036    3.9647  dev_queue_xmit
...
> What is bothering me, why getnstimeofday called so much? Even i remove HTB 
> shaper, it still takes 30-40% of whole vmlinux time. From other 
> applications - only zebra is running.
> Any ideas?

This function is really used in many places, and these profiles are
not enough at least to me, but it seems you could have a lot of
softirqs (and probably hrtimers) scheduling, so maybe you should try
if e.g. disabling hrtimers or changing kernel HZ makes any difference.

Jarek P.
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