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/
Home Products Support Community News


Re: [Xen-devel] [RFC] Scheduler work, part 1: High-level goals and inter

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] Scheduler work, part 1: High-level goals and interface.
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 17 Apr 2009 09:17:29 -0700
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "Tian, Kevin" <kevin.tian@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Fri, 17 Apr 2009 09:17:54 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <1cd8b7d4-37bc-41c5-923d-c7bb3f565072@default>
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/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <1cd8b7d4-37bc-41c5-923d-c7bb3f565072@default>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Thunderbird (X11/20090320)
Dan Magenheimer wrote:
And that's the oversimplification I think.  Just
because Intel provides a rule-of-thumb that the extra
thread increases performance by 30% doesn't mean that
it is a good number to choose for scheduling purposes.

Actually the 70% was a number I plucked out of the air with no justification at all.

I suspect (and maybe this has even already been proven)
that this varies from 0%-100% depending on the workload,
and may even vary from *negative* to *more* than 100%.
(Yes, I understand that i7 is supposed to be better than
the last round of HT... but is it always better?)

The only way to know is by measurement, ideally with some specific performance counter which tells you what went on in that last timeslice. But if this is a big issue, you can always disable HT, as lots of people did the last time around.


Xen-devel mailing list

<Prev in Thread] Current Thread [Next in Thread>