linux-kernel - Re: Network performance degradation from 2.6.11.12 to 2.6.16.20

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Date:	Sat, 16 Sep 2006 16:08:46 +0400
From:	"Vladimir B. Savkin" <master@...torb.msk.ru>
To:	Andi Kleen <ak@...e.de>
Cc:	Jesper Dangaard Brouer <hawk@...u.dk>,
	Harry Edmon <harry@...os.washington.edu>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Network performance degradation from 2.6.11.12 to 2.6.16.20

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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