Hello , <div><br></div><div>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. </div>


<div><br></div><div>I am using taskset to define the cpu-affinity of the qemu process : </div><div>taskset -p 0x1 `pgrep qemu` (assuming only 1 vm is running ) </div><div><br></div><div>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&#39;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 )</div>


<div>So why does not the output of top ( qemu is using 99% of it&#39;s cpu time , which is spent on core 0 )  co-relate with powertop ( which says core 0 is idle for around 88% of time ) ? </div><div>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 ? </div>

<div>There are no other cpu/memory intensive tasks running on the host.</div>
<div><br></div><div>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 ? </div>


<div>Also , if instead of -a , if I give -C 0 , perf just saves around 0.016MB as opposed to 1.894MB in case of -a option. If the vm is indeed using core 0 , then perf should have recorded the events. </div><div><br></div>


<div>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 ? </div><div><br></div><div>Thanks , </div>


<div>Jaspal<br><div><br></div><div><br></div>
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