Date: Sat, 16 Sep 2006 16:08:46 +0400
From: "Vladimir B. Savkin" <master@sectorb.msk.ru>
To: Andi Kleen <ak@suse.de>
Cc: Jesper Dangaard Brouer <hawk@diku.dk>,
       Harry Edmon <harry@atmos.washington.edu>, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org
Subject: Re: Network performance degradation from 2.6.11.12 to 2.6.16.20
Message-ID: <20060916120845.GA18912@tentacle.sectorb.msk.ru>
References: <4492D5D3.4000303@atmos.washington.edu> <44948EF6.1060201@atmos.washington.edu> <Pine.LNX.4.61.0606191638550.23553@ask.diku.dk> <200606191724.31305.ak@suse.de>
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On Mon, Jun 19, 2006 at 05:24:31PM +0200, Andi Kleen wrote:
> 
> > If you use "pmtmr" try to reboot with kernel option "clock=tsc".
> 
> That's dangerous advice - when the system choses not to use
> TSC it often has a reason.

I just found out that TSC clocksource is not implemented on x86-64.
Kernel version 2.6.18-rc7, is it true?

I've also had experience of unsychronized TSC on dual-core Athlon,
but it was cured by idle=poll.

> 
> > 
> > On my Opteron AMD system i normally can route 400 kpps, but with 
> > timesource "pmtmr" i could only route around 83 kpps.  (I found the timer 
> > to be the issue by using oprofile).
> 
> Unless you're using packet sniffing or any other application
> that requests time stamps on a socket then the timer shouldn't 
> make much difference. Incoming packets are only time stamped
> when someone asks for the timestamps.
> 
It seems that dhcpd3 makes the box timestamping incoming packets,
killing the performance. I think that combining router and DHCP server
on a same box is a legitimate situation, isn't it?

~
:wq
                                        With best regards, 
                                           Vladimir Savkin. 

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