Re: Invalid event (cycles:pp) in per-thread mode, enable system wide with '-a'.

[Namhyung Kim]

Hi Nick,

On Fri, Jun 23, 2023 at 9:23 AM Nick Desaulniers
<ndesaulniers@xxxxxxxxxx> wrote:
>
> On Tue, Oct 11, 2022 at 10:05 PM Ravi Bangoria <ravi.bangoria@xxxxxxx> wrote:
> >
> > On 12-Oct-22 9:36 AM, Ravi Bangoria wrote:
> > > On 12-Oct-22 3:02 AM, Nick Desaulniers wrote:
> > >> On Thu, Oct 6, 2022 at 8:56 PM Ravi Bangoria <ravi.bangoria@xxxxxxx> wrote:
> > >>>
> > >>> +cc: PeterZ
> > >>>
> > >>>>>>>> +Ravi who may be able to say if there are any issues with the precise
> > >>>>>>>> sampling on AMD.
> > >>>>>>>
> > >>>>>>> Afaik cvcles:pp will use IBS but it doesn't support per-task profiling
> > >>>>>>> since it has no task context.  Ravi is working on it..
> > >>>>>>
> > >>>>>> Right.
> > >>>>>> https://lore.kernel.org/lkml/20220829113347.295-1-ravi.bangoria@xxxxxxx
> > >>>>>
> > >>>>> Cool, thanks for working on this Ravi.
> > >>>>>
> > >>>>> I'm not sure yet whether I may replace the kernel on my corporate
> > >>>>> provided workstation, so I'm not sure yet I can help test that patch.
> > >>>>>
> > >>>>> Can you confirm that
> > >>>>> $ perf record -e cycles:pp --freq=128 --call-graph lbr -- <command to profile>
> > >>>>>
> > >>>>> works with just that patch applied? Or is there more work required?
> > >>>>> What is the status of that patch?
> > >>>>>
> > >>>>> For context, we had difficulty upstreaming support for instrumentation
> > >>>>> based profile guided optimizations in the Linux kernel.
> > >>>>> https://lore.kernel.org/lkml/CAHk-=whqCT0BeqBQhW8D-YoLLgp_eFY=8Y=9ieREM5xx0ef08w@xxxxxxxxxxxxxx/
> > >>>>> We'd like to be able to use either instrumentation or sampling to
> > >>>>> optimize our builds.  The major barrier to sample based approaches are
> > >>>>> architecture / micro architecture issues with sample based profile
> > >>>>> data collection, and bitrot of data processing utilities.
> > >>>>> https://github.com/google/autofdo/issues/144
> > >>>>
> > >>>> On existing AMD Zen2, Zen3 the following cmdline:
> > >>>> $ perf record -e cycles:pp --freq=128 --call-graph lbr -- <command to profile>
> > >>>>
> > >>>> does not work. I see two reasons:
> > >>>>
> > >>>> 1. cycles:pp is likely converted into IBS op in cycle mode.
> > >>>>     Current kernels do not support IBS in per-thread mode.
> > >>>>     This is purely a kernel limitation
> > >>>
> > >>> Right, it's purely a kernel limitation. And below simple patch on top
> > >>> of event-context rewrite patch[1] should be sufficient to make cycles:pp
> > >>> working in per-process mode on AMD Zen.
> > >>>
> > >>> ---
> > >>> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> > >>> index c251bc44c088..de01b5d27e40 100644
> > >>> --- a/arch/x86/events/amd/ibs.c
> > >>> +++ b/arch/x86/events/amd/ibs.c
> > >>> @@ -665,7 +665,7 @@ static struct perf_ibs perf_ibs_fetch = {
> > >>>
> > >>>  static struct perf_ibs perf_ibs_op = {
> > >>>         .pmu = {
> > >>> -               .task_ctx_nr    = perf_invalid_context,
> > >>> +               .task_ctx_nr    = perf_hw_context,
> > >>>
> > >>>                 .event_init     = perf_ibs_init,
> > >>>                 .add            = perf_ibs_add,
> > >>> ---
> > >>>
> > >>> [1]: https://lore.kernel.org/lkml/20220829113347.295-1-ravi.bangoria@xxxxxxx
> > >>
> > >> Hi Ravi,
> > >> I didn't see the above diff in
> > >> https://lore.kernel.org/lkml/20221008062424.313-1-ravi.bangoria@xxxxxxx/
> > >> Was there another distinct patch you were going to send for the above?
> > >
> > > Yes Nick. I was planning to send it once the rewrite stuff goes in.
> >
> > Hi Nick,
> >
> > Since you have practical use case, would it be possible to run your workflow
> > with perf rewrite and IBS patches applied? It will help us in finding/fixing
> > more bugs and upstreaming these changes.
>
> Hi Ravi,
> Sorry, I'm not able to load a custom kernel image on my employer
> provided workstation, and I never got approval to expense hardware for
> testing this otherwise.
>
> Was there ever any update on this? I'm on 6.1.25 now and still cant run
> $ perf record -e cycles:pp --call-graph lbr <any command to profile>
> $ cat /proc/cpuinfo
> ...
> model name      : AMD Ryzen Threadripper PRO 3995WX 64-Cores
> ...

The commit 30093056f7b2 ("perf/amd/ibs: Make IBS a core pmu") in v6.2.

  $ git name-rev --tags --refs=v[2-6].* 30093056f7b2
  30093056f7b2 v6.2-rc1~176^2~16

https://git.kernel.org/torvalds/c/30093056f7b2

Thanks,
Namhyung