Re: loaded router, excessive getnstimeofday in oprofile

Andi Kleen
2008-08-27T16:54:27Z

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.

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