From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jaspal Subject: Re: Using taskset , powertop and perf with qemu-kvm Date: Wed, 10 Oct 2012 17:50:21 +0530 Message-ID: <50756805.8080009@gmail.com> References: <50752936.7070703@gmail.com> <20121010100844.GD23096@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:54102 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751899Ab2JJMU0 (ORCPT ); Wed, 10 Oct 2012 08:20:26 -0400 Received: by mail-pb0-f46.google.com with SMTP id rr4so650238pbb.19 for ; Wed, 10 Oct 2012 05:20:26 -0700 (PDT) In-Reply-To: <20121010100844.GD23096@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 10/10/2012 03:38 PM, Gleb Natapov wrote: > On Wed, Oct 10, 2012 at 01:22:22PM +0530, Jaspal wrote: >> Hello , >> >> I wish to run some cpu intensive tasks on a vm , use only one core >> specifically #0 of the 6 available ( Xeon 3670 ) and all the while >> record basic perf events like cpu-cycles , instructions etc. >> >> I am using taskset to define the cpu-affinity of the qemu process : >> taskset -p 0x1 `pgrep qemu` (assuming only 1 vm is running ) >> > pgrep tells you only the pid of the io thread. vcpu runs in a separate > thread. > >> I can verify that the vm is now running only on core 0 using top. >> top also shows that the qemu process is using 99% of it's share of >> CPU time ( %CPU column in top ) upon running the tasks in vm. >> However what I fail to see is the increase in time spent of the core >> 0 in the C0 ( active ) state via powertop. It barely manages to >> cross 12%. If I run the same tasks ( FFT benchmark ) on the host on >> a different core ( say #1 ) and monitor it using powertop again , I >> can see that C0 % for core 1 is above 100% ( 104 ~ 107 ) >> So why does not the output of top ( qemu is using 99% of it's cpu >> time , which is spent on core 0 ) co-relate with powertop ( which >> says core 0 is idle for around 88% of time ) ? >> Also , powertop reports that core 2 is being used heavily ( 104 % ) >> and I suspect this is one which is executing the vm operations. But >> why ? >> There are no other cpu/memory intensive tasks running on the host. >> >> Next , I am using the perf kvm record function to save the stats. If >> I use all the 7 core counters available along-with -a option , perf >> generates ~2MB/second . Is there a way to save just the raw count of >> the events ? >> Also , if instead of -a , if I give -C 0 , perf just saves around >> 0.016MB/s as opposed to 1.894MB/s in case of -a option. If the vm is >> indeed using core 0 , then perf should have recorded the events. >> >> On a last note , does perf kvm automatically selects the vm to >> profile ( in case multiple vms are running ) on the basis of the >> guest.kallsyms and guest.modules files passed to it ? >> >> Thanks , >> Jaspal >> -- >> To unsubscribe from this list: send the line "unsubscribe kvm" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > Gleb. Thanks. It works using the correct tid. -- Jaspal