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Message-ID: <48B58792.5080501@hp.com>
Date: Wed, 27 Aug 2008 09:57:54 -0700
From: Rick Jones <rick.jones2@...com>
To: Andi Kleen <andi@...stfloor.org>
CC: 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
Andi Kleen wrote:
> On Wed, Aug 27, 2008 at 09:49:10AM -0700, Rick Jones wrote:
>
>>Andi Kleen wrote:
>>
>>>>Those banks really want to crank down on latency - to the point they
>>>>start disabling interrupt coalescing. I bet they'd toss anything out
>>>>they could to shave another microsecond.
>>>
>>>
>>>This change would actually likely lower their latency.
>>
>>I'm guessing you mean increase their latency? I agree, it could -
>>depends entirely on the PPS in production I suspect.
>
>
> No, moving the time stamps into the socket decreases latency
> for all packets that don't need time stamps. And they likely
> have some packets which don't need time stamps too.
Ah, since that part of the discussion wasn't in the quoted text I
assumed you were talking about the disabling of interrupt coalescing.
rick jones
>
> As a secondary effect if they use a RT kernel it might
> be also beneficial to do the (depending on the platform)
> costly time stamp in the lower priority socket context
> than in the high priority interrupt thread.
>
> -Andi
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