Re: loaded router, excessive getnstimeofday in oprofile

Denys Fedoryshchenko
2008-08-28T20:01:27Z

On Thursday 28 August 2008, David Miller wrote:
> From: Denys Fedoryshchenko <denys@visp.net.lb>
> Date: Thu, 28 Aug 2008 19:48:52 +0300
>
> > So there is few good solutions available (IMHO):
> > 1)Introduce some SO_REALTIMESTAMP (anyway even SO_TIMESTAMP not defined
> > in any standard) for banks and ntp folks, who need them. And even give
> > them timespec instead timeval, so they will be even more happy with
> > resolution. 2)Provide sysctl,kernel boot, or even "build time" option for
> > "banks" to have high resolution(and expensive) SO_TIMESTAMP.
>
> The performance hit hurts, but changing the default to lower
> resolution after it having been high resolution for 10+ years
> is a regression and something we really can't do.
Agree. Then maybe to add way to choose, because choice is high resolution vs
performance. For example Intel dynamically throttling interrupts on e1000*,
and it saves me in this case. They leave also option for users who wants low
latency/high troughput.
So maybe there must be a way for specific functions who uses get(ns)timeofday
to use specific timers (cheap and less precise), by option. Or to limit
amount of calls to timer by them.