Re: [Patch 1/4] Delay accounting: Initialization

Marcelo Tosatti
2005-11-15T17:32:19Z

On Tue, Nov 15, 2005 at 10:19:17AM -0500, Shailabh Nagar wrote:
> Marcelo Tosatti wrote:
> > On Mon, Nov 14, 2005 at 08:20:17PM -0800, Andrew Morton wrote:
> >
> >>Shailabh Nagar <nagar@watson.ibm.com> wrote:
> >>
> >>>+ *ts = sched_clock();
> >>
> >>I'm not sure that it's kosher to use sched_clock() for fine-grained
> >>timestamping like this. Ingo had issues with it last time this happened?

Maybe Ingo had some other issue other than !use_rtc ? Better check.

> > If the system boots with use_rtc == 0 you're going to get jiffies based
> > resolution from sched_clock(). I have a 1GHz Pentium 3 around here which
> > does that.
>
> Good point, thanks. This reemphasizes the need for better normalization
> at output time.

> > Maybe use do_gettimeofday() for such systems?
>
> Perhaps getnstimeofday() so resolution isn't reduced to msec level unnecessarily.
> In these patches, userspace takes responsibility for handling wraparound so
> delivering a reasonably high-resolution delay data from the kernel is preferable.
>
> >
> > Would be nice to have a sort of per-arch overridable "gettime()" function?
> >
>
> Provided as part of this patch ?

Yep, think so. My comment meant that its nice to hide away architecture
speficic code from generic code, so you don't have to add #ifdef's and
such.

Not sure about the nicer way to do that.