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@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
