WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] Power aware credit scheduler

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Power aware credit scheduler
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 19 Jun 2008 08:31:55 +0100
Cc: ackaouy@xxxxxxxxx, "Wei, Gang" <gang.wei@xxxxxxxxx>, "Yu, Ke" <ke.yu@xxxxxxxxx>
Delivery-date: Thu, 19 Jun 2008 00:31:22 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <D470B4E54465E3469E2ABBC5AFAC390F024D9444@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcjRyDPly+hYayDgSN6PPLduSJGRXQAFliV6
Thread-topic: [Xen-devel] Power aware credit scheduler
User-agent: Microsoft-Entourage/11.4.0.080122
On 19/6/08 05:51, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> b) when physical cpu resides in idle C-state
> Avoid unnecessary work to keep longer C-state residency.
> For example, accouting process (tick timer, more specifically)
> can be stopped before C-state entrance and then resumed after
> waking up. The point is that no accounting is required when current
> cpu is idle, and any runqueue change triggering from other cpus
> incurs a IPI to this cpu which effectively breaks it back to C0
> state with accounting resumed. Since the residency period may
> be longer than accouting period (30ms), csched_tick should be
> aware of resume event to adjust elapsed credits.

Yes, this should be an easy low-hanging fruit to fix.

> c) when cpu's freq is scaled dynamically
> When cpufreq/Px is enabled, cpu's frequency is adjusted
> to different operation points driven by a on-demand governor. So
> csched_acct may need take frequency difference among cpus into
> consideration and total available credits won't be a simple 300 *
> online cpu_number.

Not sure. I think the current governor runs frequently to react to the
scheduler (i.e., try to keep the CPU non-idle by downscaling frequency;
upscale frequency when the CPU gets busy; both these done over sub-second
timescales). Does it then make sense to have the scheduler react to
governor? Sounds like it could be a weird feedback loop.

 -- Keir



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel