From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: Performance difference between Xen versions Date: Mon, 02 May 2011 10:00:38 +0200 Message-ID: <4DBE64A6.2080602@ts.fujitsu.com> References: <4DBE41C9.1010409@ts.fujitsu.com> <4DBE7819020000780003F1B6@vpn.id2.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4DBE7819020000780003F1B6@vpn.id2.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: Keir Fraser , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 05/02/11 09:23, Jan Beulich wrote: >>>> On 02.05.11 at 08:41, Keir Fraser wrote: >> On 02/05/2011 06:31, "Juergen Gross" wrote: >> >>>>> Is there any easy explanation for this? Both Xen versions are from SLES >>>>> (SLES11 or SLES11 SP1). >>>> I think cpufreq handling was off by default in 3.3, and is on by >>>> default on 4.0. Try turning this off, or using the performance >>>> governor. >>> Jan, you got it! With cpufreq=none Xen 4.0 has more or less the same numbers >>> as 3.3. Now I wonder why the default is so much slower. I looks as if the >>> hypervisor would run at a lower speed. I can't believe it should behave like >>> that! >> It runs at lower frequency unless your test offers sufficient load over a >> long enough time period. Short microbenchmarks are probably finished before >> the frequency governor can react. > Correct. I generally found the default threshold of the ondemand > governor nor very suitable for optimal performance of short lived > jobs, and boot all of my systems with "cpufreq=xen:ondemand,threshold=20". Thanks, Keir and Jan! You both helped me a lot! I think the short term solution for our problem is to disable the cpufreq governor on our BS2000 machines. On the long run I'd like to make the cpufreq governor a feature of the cpupool. This would enable an administrator of a large Xen machine with a heterogeneous load to specify which domains should run at full speed and which are allowed to save energy at the cost of latency. What do you think? Juergen -- Juergen Gross Principal Developer Operating Systems TSP ES&S SWE OS6 Telephone: +49 (0) 89 3222 2967 Fujitsu Technology Solutions e-mail: juergen.gross@ts.fujitsu.com Domagkstr. 28 Internet: ts.fujitsu.com D-80807 Muenchen Company details: ts.fujitsu.com/imprint.html