From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [RFC] Scheduler work, part 1: High-level goals and interface. Date: Fri, 17 Apr 2009 09:17:29 -0700 Message-ID: <49E8AB99.5060001@goop.org> References: <1cd8b7d4-37bc-41c5-923d-c7bb3f565072@default> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1cd8b7d4-37bc-41c5-923d-c7bb3f565072@default> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Dan Magenheimer Cc: George Dunlap , "Tian, Kevin" , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org 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. J