From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Performance difference between Xen versions Date: Fri, 29 Apr 2011 14:28:10 +0100 Message-ID: References: <4DBAAFF1.8080001@ts.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4DBAAFF1.8080001@ts.fujitsu.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: Juergen Gross , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org Are you sure TSC runs at the same rate in the guest on both hypervisor versions? Xen 4.0 might trap and emulate a more consistent but slower rate TSC by default. 'tsc_mode=2' in your domain config file on 4.0 might be a quick fix. -- Keir On 29/04/2011 13:32, "Juergen Gross" wrote: > Hi, > > comparing performance of different Xen versions with BS2000 as HVM guest > showed some weird data I'd like to understand. > > All measurements were done on an Intel Xeon E7220 box. We used a disk- > benchmark and found the cpu utilization was much higher with Xen 4.0 compared > to Xen 3.3. I did some more investigation and narrowed things down to calls of > the hypervisor (implicit or explicit). > > Following is a table with timing data for different low-level functions, all > timing values are tsc ticks obtained via rdtsc: > > Xen 3.3 Xen 4.0 Function > 88 165 just the measurement overhead > 176 330 rdtsc-instruction + cli/sti > 5896 11044 lapic timer query > 7381 13519 setting lapic timer > 4653 8987 reload of cr3 > 3124 5709 invlpg instruction > 792253 792264 wbinvd instruction > 748 1375 int + iret > 5203 9317 hypervisor yield call > 12598102 12597882 memory access loop > > All operations involving the hypervisor take nearly twice the time on 4.0. > Operations not involving the hypervisor (wbinvd and memory access loop) are > the same on both systems (this rules out the possibility of different rdtsc > behavior). > > Is there any easy explanation for this? Both Xen versions are from SLES > (SLES11 or SLES11 SP1). > > > Juergen