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

Marcelo Tosatti
2005-11-15T17:46:18Z

On Tue, Nov 15, 2005 at 10:20:35AM -0200, Marcelo Tosatti wrote:
> 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.
Yep.
> > 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.

Actually I dont think there is any kind of "get_timestamp()" style
API now. Maybe it would be nice to create one? Its generic functionality
after all.

blktrace is also using sched_clock(), too.

> 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.
>
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