From: Nick Piggin <npiggin@suse.de>
To: Arjan van de Ven <arjan@infradead.org>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
linux-arch@vger.kernel.org
Subject: Re: [patch] Remove the per cpu tick skew
Date: Fri, 30 Jul 2010 17:27:04 +1000 [thread overview]
Message-ID: <20100730072704.GA9960@amd> (raw)
In-Reply-To: <20100727210210.58d3118c@infradead.org>
On Tue, Jul 27, 2010 at 09:02:10PM -0700, Arjan van de Ven wrote:
> Hi,
>
> the following patch is a win for power management on x86....
> ... but since this touches generic code.. are there any
> other architectures that would be negatively affected by this?
>
>
>
> Subject: [patch] Remove the per cpu tick skew
>
> Historically, Linux has tried to make the regular timer tick on the various
> CPUs not happen at the same time, to avoid contention on xtime_lock.
>
> Nowadays, with the tickless kernel, this contention no longer happens
> since time keeping and updating are done differently. In addition,
> this skew is actually hurting power consumption in a measurable
> way on many-core systems.
Question, how much of a win is it? What does it do that tickless
idle does not, can you explain?
>
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
>
> --- linux.trees.git/kernel/time/tick-sched.c~ 2010-07-16 09:40:50.000000000 -0400
> +++ linux.trees.git/kernel/time/tick-sched.c 2010-07-26 11:18:51.138003329 -0400
> @@ -780,7 +780,6 @@
> {
> struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
> ktime_t now = ktime_get();
> - u64 offset;
>
> /*
> * Emulate tick processing via per-CPU hrtimers:
> @@ -790,10 +789,6 @@
>
> /* Get the next period (per cpu) */
> hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
> - offset = ktime_to_ns(tick_period) >> 1;
> - do_div(offset, num_possible_cpus());
> - offset *= smp_processor_id();
> - hrtimer_add_expires_ns(&ts->sched_timer, offset);
>
> for (;;) {
> hrtimer_forward(&ts->sched_timer, now, tick_period);
>
> --
> Arjan van de Ven Intel Open Source Technology Centre
> For development, discussion and tips for power savings,
> visit http://www.lesswatts.org
> --
> To unsubscribe from this list: send the line "unsubscribe linux-arch" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2010-07-30 7:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-28 4:02 [patch] Remove the per cpu tick skew Arjan van de Ven
2010-07-28 20:26 ` john stultz
2010-07-28 23:50 ` john stultz
2010-07-30 7:27 ` Nick Piggin [this message]
2010-07-30 13:57 ` Arjan van de Ven
2010-08-02 19:48 ` [tip:timers/core] clockevents: " tip-bot for Arjan van de Ven
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=20100730072704.GA9960@amd \
--to=npiggin@suse.de \
--cc=arjan@infradead.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=tglx@linutronix.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.