Re: [Xen-devel] How to make tracking CPU cache-miss on Xen?

[Meng Xu <xumengpanda@xxxxxxxxx>]

On Mon, Dec 11, 2017 at 8:14 AM, Minjun Hong <nickeysgo@xxxxxxxxx> wrote:
>
> Thanks for your answer, George.
>
> What I want ultimately is cache misses from the guest, but even I could not 
> get the cache misses from dom0 also.
> That's why I'm confused as I know, it should be possible to get cache-misses 
> from dom0 (is it right??).
> I already enabled CONFIG_XEN_HAVE_VPMU of current kernel to get cache misses. 
> Is there anything what I miss during Xen install?
>

If this is for a research project, I would suggest you to write your
own code to monitor the cache misses for domU. This could be faster,
since it's not complicated to do so.

IIRC, PMU in Xen can only monitor the cache misses when VCPUs are
pinned to cores.


Best Regards,

Meng

-----------
Meng Xu
Ph.D. Candidate in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/
>
>
> On Mon, Dec 11, 2017 at 7:54 PM, George Dunlap <dunlapg@xxxxxxxxx> wrote:
>>
>> On Mon, Dec 11, 2017 at 5:59 AM, Minjun Hong <nickeysgo@xxxxxxxxx> wrote:
>> > Hello, I'm working on the 'credit scheduler' of Xen.
>> > And I need to compare CPU cache misses between original Xen and my patching
>> > version.
>> > But I failed all attempt even if I have tried many methods by googling.
>> > When I typed 'perf list' with my 'perf' compiled by source code in the
>> > current kernel source code, it said:
>> >
>> >> nickeys@nickeys-linux-machine:~/ubuntu/tools/perf$ ./perf list
>> >> List of pre-defined events (to be used in -e):
>> >>   msr/pperf/                                         [Kernel PMU event]
>> >>   msr/smi/                                           [Kernel PMU event]
>> >>   msr/tsc/                                           [Kernel PMU event]
>> >>   power/energy-cores/                                [Kernel PMU event]
>> >>   power/energy-gpu/                                  [Kernel PMU event]
>> >>   power/energy-pkg/                                  [Kernel PMU event]
>> >>   power/energy-psys/                                 [Kernel PMU event]
>> >>   power/energy-ram/                                  [Kernel PMU event]
>> >>   rNNN                                               [Raw hardware event
>> >> descriptor]
>> >>   cpu/t1=v1[,t2=v2,t3 ...]/modifier                  [Raw hardware event
>> >> descriptor]
>> >>    (see 'man perf-list' on how to encode it)
>> >>   mem:<addr>[/len][:access]                          [Hardware breakpoint]
>> >> nickeys@nickeys-linux-machine:~/ubuntu/tools/perf$
>> >
>> >
>> >
>> > Since there is no HW event in contrast with native environment, I should 
>> > try
>> > 'Raw hardware event descriptor' option.
>> > According to 'Intel® 64 and IA-32 Architectures Software Developer’s Manual
>> > Volume 3B: System Programming Guide', I used 'r412e' raw hardware event to
>> > get LLC Misses which is in '18.2.1.2 Pre-defined Architectural Performance
>> > Events' section of the guide,
>> > but I found out my 'perf' does not support the feature:
>> >
>> >> nickeys@nickeys-linux-machine:~/ubuntu/tools/perf$ sudo ./perf stat -e
>> >> r412e sleep 1
>> >>  Performance counter stats for 'sleep 1':
>> >>    <not supported>      r412e
>> >>        1.002120111 seconds time elapsed
>> >> nickeys@nickeys-linux-machine:~/ubuntu/tools/perf$
>> >
>> >
>> >  I could not understand why I cannot find out the number of cache-misses.
>> > When I did googling, I did not think there would be a problem because there
>> > were a lot of posts to get cache-misses in the Xen environment.
>>
>> It sounds like what you might want is the vPMU functionality.  CC'ing
>> Boris Ostrovsky, who has worked on vPMU functionality before.
>>
>> However, are you sure that you want to be reading cache misses from
>> the guest?  It seems like that is *probably* OK, but another option
>> would be to instrument Xen to read and provide that information.
>>
>>  -George
>
>
>
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