netdev - Re: loaded router, excessive getnstimeofday in oprofile

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Date:	Wed, 27 Aug 2008 19:14:31 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Eric Dumazet <dada1@...mosbay.com>,
	Denys Fedoryshchenko <denys@...p.net.lb>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: loaded router, excessive getnstimeofday in oprofile

Stephen Hemminger wrote, On 08/27/2008 06:17 PM:

> On Wed, 27 Aug 2008 14:54:12 +0200
> Andi Kleen <andi@...stfloor.org> wrote:
> 
>> Evgeniy Polyakov <johnpol@....mipt.ru> writes:
>>> Yup, this innocent toys can end up with this such behaviour on modern
>>> highly loaded machines.
>> I and also other people had some patches to move the time stamp
>> measuring into the socket. This way the time stamping didn't need to
>> be enabled on all packets, only on those that actually end up at a
>> socket that requires the time stamp.
>>
>> Unfortunately DaveM didn't like it because some bank wanted
>> different semantics, see the discussion in 
>> http://thread.gmane.org/gmane.linux.network/91679
>>
>> Perhaps you can find out which bank it was and send them a bill for
>> your CPU time ;-)
>>
>> -Andi
>>
> 
> Look at /proc/net/ptype to see if any AF_PACKET sockets are open.
> There are several causes of this:
>    * Applications like DHCP use AF_PACKET when they could use something else
>    * AF_PACKET API was poorly designed and always has timestamps
>    * The choice was made to get more accurate timestamps by stamping early in
>      receive code. A better alternative would be to do it in protocol handler
>      after the socket filter. Sorry, Andi socket layer is too late.
>    * No driver is using hardware mechanisms to get accurate/free timestamps.
>      I was working on sky2, but never was stable/complete.
> 
> Easist advice now is to fix userspace.

And what is working advice?

Why exactly admin can't chose between 2 alternatives here?

Jarek P.
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