From: Pierre Ossman <drzeus-list@drzeus.cx>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Jesper Juhl <jesper.juhl@gmail.com>, Dominik Brodowski <linux@brodo.de>
Subject: [Fwd: sched_clock() has poor resolution]
Date: Thu, 22 Sep 2005 09:28:49 +0200 [thread overview]
Message-ID: <43325D31.3090604@drzeus.cx> (raw)
cc:ing some timer hackers.
-------- Original Message --------
Subject: sched_clock() has poor resolution
Date: Tue, 20 Sep 2005 12:02:34 +0200
From: Pierre Ossman <drzeus-list@drzeus.cx>
To: LKML <linux-kernel@vger.kernel.org>
I've been trying to hunt down a HZ bug and as part of that I thought
having printk timestamps would be nice. But too much dismay I noticed
that I couldn't get very good resolution out of these.
The problem turned out to be that sched_clock() uses jiffies as a time
source. It will only use the TSC if that's the primary time source of
the system. But since I have a PM timer that is given priority.
So I see two solutions here:
* Let sched_clock() follow the time source. Don't have it coupled to
the TSC.
* Init the TSC even though it isn't used for anything but sched_clock().
The first solution might have problems if one of the "better" timers are
slow as hell to read and the second if there is some assumed dependency
between sched_clock() and the primary timer. I'm blisfully ignorant of
this area so input is welcome.
Rgds
Pierre
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
next reply other threads:[~2005-09-22 7:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-22 7:28 Pierre Ossman [this message]
2005-09-22 20:59 ` [Fwd: sched_clock() has poor resolution] Dominik Brodowski
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=43325D31.3090604@drzeus.cx \
--to=drzeus-list@drzeus.cx \
--cc=jesper.juhl@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@brodo.de \
/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).