Re: loaded router, excessive getnstimeofday in oprofile

Rick Jones
2008-08-27T16:58:47Z

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