All of lore.kernel.org
 help / color / mirror / Atom feed
From: Andy Lutomirski <luto@amacapital.net>
To: Frederic Weisbecker <fweisbec@gmail.com>, Alex Shi <alex.shi@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	John Stultz <john.stultz@linaro.org>,
	Kevin Hilman <khilman@linaro.org>
Subject: Re: [RFC PATCH 00/13] nohz: Use sysidle detection to let the timekeeper sleep
Date: Wed, 18 Dec 2013 13:29:53 -0800	[thread overview]
Message-ID: <52B213D1.1000104@mit.edu> (raw)
In-Reply-To: <20131218174355.GA19788@localhost.localdomain>

On 12/18/2013 09:43 AM, Frederic Weisbecker wrote:
> On Wed, Dec 18, 2013 at 10:04:43AM +0800, Alex Shi wrote:
>> On 12/18/2013 06:51 AM, Frederic Weisbecker wrote:
>>> So this is what this series brings, more details following:
>>>
>>> * Some code, naming and whitespace cleanups
>>>
>>> * Allow all CPUs outside the nohz_full range to handle the timekeeping
>>>   duty, not just CPU 0. Balancing the timekeeping duty should improve
>>>   powersavings.
>>
>> If the system just has one nohz_full cpu running, it will need another
>> cpu to do timerkeeper job. Then the system roughly needs 2 cpu living.
>> From powersaving POV, that is not good compare to normal nohz idle.
> 
> Sure, but everything has a tradeoff :)
> 
> We could theoretically run with the timekeeper purely idle if the other
> CPU in full dynticks mode runs in userspace for a long while and seldom
> do syscalls and faults. Timekeeping could be updated on kernel/user
> boundaries in this case without much impact on performances.
> 
> But then there is one strict condition for that: it can't read the timeofday
> through the vdso but only through a syscall.

Where's your ambition? :)

If the vdso timing functions could see that it's been too long since a
real timekeeping update, they could fall back to a syscall.  Otherwise,
they could using rdtsc or whatever is in use.

--Andy

  reply	other threads:[~2013-12-18 21:30 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-12-17 22:51 [RFC PATCH 00/13] nohz: Use sysidle detection to let the timekeeper sleep Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 01/13] tick: Rename tick_check_idle() to tick_irq_enter() Frederic Weisbecker
2014-01-25 14:22   ` [tip:timers/urgent] " tip-bot for Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 02/13] time: New helper to check CPU eligibility to handle timekeeping Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 03/13] rcu: Exclude all potential timekeepers from sysidle detection Frederic Weisbecker
2013-12-17 23:27   ` Paul E. McKenney
2013-12-17 23:49     ` Frederic Weisbecker
2013-12-18 11:43       ` Peter Zijlstra
2013-12-18 11:46         ` Peter Zijlstra
2013-12-18 14:15         ` Paul E. McKenney
2013-12-18 16:24         ` Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 04/13] tick: Use timekeeping_cpu() to elect the CPU handling timekeeping duty Frederic Weisbecker
2013-12-17 23:55   ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 05/13] rcu: Fix unraised IPI to timekeeping CPU Frederic Weisbecker
2013-12-17 23:21   ` Paul E. McKenney
2013-12-18 14:13     ` Frederic Weisbecker
2013-12-18 14:22       ` Paul E. McKenney
2013-12-18 14:56         ` Frederic Weisbecker
2013-12-18 15:11           ` Peter Zijlstra
2013-12-18 15:58             ` Frederic Weisbecker
2013-12-18 12:12   ` Peter Zijlstra
2013-12-18 15:38     ` Frederic Weisbecker
2013-12-18 15:45       ` Christoph Hellwig
2013-12-18 17:10       ` Peter Zijlstra
2013-12-17 22:51 ` [PATCH 06/13] nohz: Introduce full dynticks' default timekeeping target Frederic Weisbecker
2013-12-17 23:54   ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 07/13] sched: Enable IPI reception on timekeeper under nohz full system Frederic Weisbecker
2013-12-17 23:52   ` Paul E. McKenney
2013-12-18 14:49     ` Frederic Weisbecker
2013-12-18 15:50       ` Paul E. McKenney
2013-12-18 10:06   ` Peter Zijlstra
2013-12-17 22:51 ` [PATCH 08/13] nohz: Get timekeeping max deferment outside jiffies_lock Frederic Weisbecker
2014-01-25 14:22   ` [tip:timers/urgent] " tip-bot for Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 09/13] nohz: Allow timekeeper's tick to stop when all full dynticks CPUs are idle Frederic Weisbecker
2013-12-17 23:51   ` Paul E. McKenney
2013-12-18 14:36     ` Frederic Weisbecker
2013-12-18 15:29       ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 10/13] nohz: Hand over timekeeping duty on cpu offlining Frederic Weisbecker
2013-12-17 23:40   ` Paul E. McKenney
2013-12-18 14:19     ` Frederic Weisbecker
2013-12-18 12:30   ` Peter Zijlstra
2013-12-18 16:43     ` Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 11/13] nohz: Wake up timekeeper on exit from sysidle state Frederic Weisbecker
2013-12-17 23:34   ` Paul E. McKenney
2013-12-17 23:52     ` Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 12/13] nohz: Allow all CPUs outside nohz_full range to do timekeeping Frederic Weisbecker
2013-12-17 23:32   ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 13/13] nohz_full: fix code style issue of tick_nohz_full_stop_tick Frederic Weisbecker
2013-12-18  2:04 ` [RFC PATCH 00/13] nohz: Use sysidle detection to let the timekeeper sleep Alex Shi
2013-12-18 10:19   ` Peter Zijlstra
2013-12-18 14:18     ` Paul E. McKenney
2013-12-18 17:43   ` Frederic Weisbecker
2013-12-18 21:29     ` Andy Lutomirski [this message]
2013-12-18 21:49       ` Paul E. McKenney
2013-12-18 21:53         ` Andy Lutomirski
2013-12-18 21:57           ` Paul E. McKenney
2013-12-18 22:55             ` Andy Lutomirski

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=52B213D1.1000104@mit.edu \
    --to=luto@amacapital.net \
    --cc=alex.shi@linaro.org \
    --cc=fweisbec@gmail.com \
    --cc=john.stultz@linaro.org \
    --cc=khilman@linaro.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.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.