linux-kernel - Re: A few questions and issues with dynticks, NOHZ and powertop

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100405164023.GD2525@linux.vnet.ibm.com>
Date:	Mon, 5 Apr 2010 09:40:23 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Dominik Brodowski <linux@...inikbrodowski.net>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Dmitry Torokhov <dtor@...l.ru>
Subject: Re: A few questions and issues with dynticks, NOHZ and powertop

On Mon, Apr 05, 2010 at 09:23:16AM -0700, Arjan van de Ven wrote:
> On 4/5/2010 9:22, Paul E. McKenney wrote:
> >On Mon, Apr 05, 2010 at 09:07:33AM -0700, Arjan van de Ven wrote:
> >>On 4/5/2010 8:14, Paul E. McKenney wrote:
> >>>So the main issue is that for many workloads, it is best to run full bore
> >>>and get done quickly, thus allowing the entire machine to be powered down?
> >>
> >>yep
> >>
> >>>If so, it seems likely that there would be some workloads that were sometimes
> >>>unable to use all the CPUs, in which case shutting down (idling, offlining,
> >>>dyntick-idling, whatever) the excess CPUs might nevertheless be the right
> >>>thing to do.
> >>
> >>but the point is that the normal scheduler + idle behavior gives you exactly that
> >>in a natural way !
> >>If you don't have enough work (tasks) to keep all cores busy, the others are and stay idle.
> >
> >So your earlier objection was not to dyntick-idle as such, but rather
> >to artificially constraining the scheduler to induce dyntick-idle?
> 
> my objection was against the notion that offlining cpus helps power/energy ;-)

Fair enough, at least in general.  I should hasten to add that Lai's
patch also helps in the case where NR_CPUS is greater than the number
of CPUs on the system.

							Thanx, Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/