From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Dan Hecht <dhecht@vmware.com>
Cc: dwalker@mvista.com, cpufreq@lists.linux.org.uk,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Con Kolivas <kernel@kolivas.org>,
Chris Wright <chrisw@sous-sol.org>,
Virtualization Mailing List <virtualization@lists.osdl.org>,
john stultz <johnstul@us.ibm.com>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Stolen and degraded time and schedulers
Date: Tue, 13 Mar 2007 21:37:59 -0700 [thread overview]
Message-ID: <45F77C27.8090604@goop.org> (raw)
In-Reply-To: <45F74515.7010808@vmware.com>
Dan Hecht wrote:
> With your previous definition of work time, would it be that:
>
> monotonic_time == work_time + stolen_time ??
(By monotonic time, I presume you mean monotonic real time.) Yes, I
suppose you could, but I don't think that's terribly useful. I think
work_time is probably most naturally measured in cpu clock cycles rather
than an actual time unit. You could convert it to ns, but I don't see
the point.
I know its a term in general use, but I don't think the term "stolen
time" is all that useful, particularly when we're talking about a more
general notion of cpu work contributing to the progress of process
execution. In the cpufreq case, time isn't "stolen" per se.
(I guess I don't like the term stolen time because you don't refer to
time spent on other processes as being stolen from your process: its
just processor time being distributed.)
> i.e. would you be defining stolen_time to include the time lost to
> processes due to the cpu running at a lower frequency? How does this
> play into the other potential users, besides sched_clock(), of stolen
> time? We should make sure that the abstraction introduced here makes
> sense in those places too.
Be specific. What other uses are there?
> For example, the stuff that happens in update_process_times(). I
> think we'd want to account the stolen time to cpustat->steal.
I guess we could do something for that. Would we account non-full-speed
cpus to it? Maybe?
How is cpustat->steal used? How does it get out to usermode?
> Also we'd probably want account for stolen time with regards to
> task_running_tick(). (Though, in the latter case, maybe we first have
> to move the scheduler away from assuming HZ rate decrementing of
> p->time_slice to get this right. i.e. remove the tick based assumption
> from the scheduler, and then maybe stolen time falls in more naturally
> when accounting time slices).
I think the important part is that sched_clock() be used to actually
compute how much time each process gets. The fact that a time quantum
gets stolen is less important. Or do you mean something else?
> I guess taking your cpufreq as an example of work_time progressing
> slower than monotonic_time (and assuming that the remaining time is
> what you would call stolen), then e.g. top would report 50% of your
> cpu stolen when you cpu is running at 1/2 max rate.
Yes. In the same way that clock modulation gates the cpu clock, the
hypervisor effectively gates the clock by giving time to other vcpus.
> And p->time_slice would decrement at 1/2 the rate it normally did when
> running at 1/2 speed. Is this the right thing to do? If so, then I
> agree it makes sense to model hypervisor stolen time in terms of your
> "work time".
Yes, that's my thought.
> But, if not, then maybe the amount of work you can get done during a
> period of time that is not stolen and the stolen time itself are
> really two different notions, and shouldn't be confused. I can see
> arguments both ways.
It seems to me like a nice opportunity to solve two problems with one
mechanism.
J
next prev parent reply other threads:[~2007-03-14 4:38 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-13 16:31 Stolen and degraded time and schedulers Jeremy Fitzhardinge
2007-03-13 20:12 ` john stultz
2007-03-13 20:32 ` Jeremy Fitzhardinge
2007-03-13 21:27 ` Daniel Walker
2007-03-13 21:59 ` Jeremy Fitzhardinge
2007-03-14 0:43 ` Dan Hecht
2007-03-14 4:37 ` Jeremy Fitzhardinge [this message]
2007-03-14 13:58 ` Lennart Sorensen
2007-03-14 15:08 ` Jeremy Fitzhardinge
2007-03-14 15:12 ` Lennart Sorensen
2007-03-14 19:02 ` Dan Hecht
2007-03-14 19:34 ` Jeremy Fitzhardinge
2007-03-14 19:45 ` Rik van Riel
2007-03-14 19:47 ` Jeremy Fitzhardinge
2007-03-14 20:02 ` Rik van Riel
2007-03-14 20:26 ` Dan Hecht
2007-03-14 20:31 ` Jeremy Fitzhardinge
2007-03-14 20:46 ` Dan Hecht
2007-03-14 21:18 ` Jeremy Fitzhardinge
2007-03-15 19:09 ` Dan Hecht
2007-03-15 19:18 ` Jeremy Fitzhardinge
2007-03-15 19:48 ` Rik van Riel
2007-03-15 19:53 ` Jeremy Fitzhardinge
2007-03-15 20:07 ` Dan Hecht
2007-03-15 20:14 ` Rik van Riel
2007-03-15 20:35 ` Dan Hecht
2007-03-16 8:59 ` Martin Schwidefsky
2007-03-14 20:38 ` Ingo Molnar
2007-03-14 20:59 ` Jeremy Fitzhardinge
2007-03-16 8:38 ` Ingo Molnar
2007-03-16 16:53 ` Jeremy Fitzhardinge
2007-03-15 5:23 ` Paul Mackerras
2007-03-15 19:33 ` Jeremy Fitzhardinge
2007-03-14 2:00 ` Daniel Walker
2007-03-14 6:52 ` Jeremy Fitzhardinge
2007-03-14 8:20 ` Zan Lynx
2007-03-14 16:11 ` Daniel Walker
2007-03-14 16:37 ` Jeremy Fitzhardinge
2007-03-14 16:59 ` Daniel Walker
2007-03-14 17:08 ` Jeremy Fitzhardinge
2007-03-14 18:06 ` Daniel Walker
2007-03-14 18:41 ` Jeremy Fitzhardinge
2007-03-14 19:00 ` Daniel Walker
2007-03-14 19:44 ` Jeremy Fitzhardinge
2007-03-14 20:33 ` Daniel Walker
2007-03-14 21:16 ` Jeremy Fitzhardinge
2007-03-14 21:34 ` Daniel Walker
2007-03-14 21:42 ` Jeremy Fitzhardinge
2007-03-14 21:36 ` Con Kolivas
2007-03-14 21:38 ` Jeremy Fitzhardinge
2007-03-14 21:40 ` Con Kolivas
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