From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Daniel Walker <dwalker@mvista.com>
Cc: john stultz <johnstul@us.ibm.com>, Andi Kleen <ak@suse.de>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
Con Kolivas <kernel@kolivas.org>,
Rusty Russell <rusty@rustcorp.com.au>,
Zachary Amsden <zach@vmware.com>,
James Morris <jmorris@namei.org>,
Chris Wright <chrisw@sous-sol.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
cpufreq@lists.linux.org.uk,
Virtualization Mailing List <virtualization@lists.osdl.org>
Subject: Re: Stolen and degraded time and schedulers
Date: Tue, 13 Mar 2007 23:52:12 -0700 [thread overview]
Message-ID: <45F79B9C.20609@goop.org> (raw)
In-Reply-To: <1173837606.23595.32.camel@imap.mvista.com>
Daniel Walker wrote:
> The adjustments that I spoke of above are working regardless of ntp ..
> The stability of the TSC directly effects the clock mult adjustments in
> timekeeping, as does interrupt latency since the clock is essentially
> validated against the timer interrupt.
>
Yep. But the tsc is just an example of a clocksource, and doesn't have
any real bearing on what I'm saying.
> like I said there are other factors so that's not going to exactly model
> cpu speed changes. You could come up with another method, but that would
> likely require another known constant clock.
>
Well, it doesn't need to be a constant clock if its modelling a changing
rate. And it doesn't need to be an exact model; it just needs to be
better than the current situation.
> sched_clock doesn't measure amounts of cpu work either, it's all about
> timing.
>
Specifically, how much cpu time a process has used. But if the CPU is
running at half speed (or 50% duty cycle), then claiming that the
process got the full amount of time is just an error.
>> Well, lots of cpus have dynamic frequencies. Any scheduler which
>> maintains history will suffer the same problem, even on UP. If
>> processes A and B are supposed to have the same priority and they both
>> execute for 1ms of real time, did they make the same amount of
>> progress? Not if the cpu changed speed in between.
>>
>
> That's true, but given a constant clock (like what sched_clock should
> have) then the accounting is similarly inaccurate. Any connection
> between the scheduler and the TSC frequency changes aren't part of the
> design AFAIK ..
>
Well, my whole argument is that sched_clock /should not/ be a constant
clock. And I'm not quite sure why you keep bringing up the tsc, because
it has no relevance.
J
next prev parent reply other threads:[~2007-03-14 6:52 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=45F79B9C.20609@goop.org \
--to=jeremy@goop.org \
--cc=ak@suse.de \
--cc=chrisw@sous-sol.org \
--cc=cpufreq@lists.linux.org.uk \
--cc=dwalker@mvista.com \
--cc=jmorris@namei.org \
--cc=johnstul@us.ibm.com \
--cc=kernel@kolivas.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=rusty@rustcorp.com.au \
--cc=tglx@linutronix.de \
--cc=virtualization@lists.osdl.org \
--cc=zach@vmware.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).