From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: CAP and performance problem Date: Thu, 6 Jun 2013 17:27:12 +0100 Message-ID: <51B0B860.1050703@eu.citrix.com> References: <519B3832.30608@di.unipmn.it> <1370451024.18519.190.camel@Solace> <1370452319.18519.197.camel@Solace> <51AF6FBD.9090007@di.unipmn.it> <1370507870.18519.224.camel@Solace> <51B04F0E.5040506@di.unipmn.it> <51B066CC.4060900@ts.fujitsu.com> <51B067F1.1010008@eu.citrix.com> <51B08606.9090105@di.unipmn.it> <51B08883.50003@ts.fujitsu.com> <51B094D1.9010806@di.unipmn.it> <1370527977.18519.275.camel@Solace> <51B0AA6A.7090704@di.unipmn.it> <1370533347.17802.8.camel@Solace> <1370534091.17802.10.camel@Solace> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1370534091.17802.10.camel@Solace> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Dario Faggioli Cc: Juergen Gross , Massimo Canonico , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 06/06/13 16:54, Dario Faggioli wrote: > On gio, 2013-06-06 at 17:42 +0200, Dario Faggioli wrote: >> Jokes apart, we may want to add a line there, perhaps on the Wiki, but I >> honestly don't think this is by any means the cap mechanism's. :-) > ^fault > > What I meant is: I don't think this can be considered cap's fault. It's certainly not cap's fault, but it wouldn't hurt to just put a comment saying something like, "NB that many systems have features that will scale down the computing power of a cpu that is not 100% utilized. This can be in the operating system, but can also sometimes be below the operating system in the BIOS. If you set a cap such that individual cores are running at less than 100%, this may have an impact on the performance of your workload over and above the impact of the cap. For example, a workload that may take 300s with a cap of 100% may take 900s with a cap of 50%, because in addition to being run only 50% of the time, the cpu is running in a lower state and so the 50% you get is less powerful. If this is a problem, look at performance and cpufreq options in our operating system and your BIOS." -George