Re: [PATCH v3] perf parse-events: Set exclude_guest=1 for user-space counting

[Like Xu]

Hi Arnaldo,

On 2020/8/17 10:32, Jin, Yao wrote:
> Hi Arnaldo,
>
> On 8/14/2020 8:47 PM, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Aug 14, 2020 at 09:21:20AM +0800, Jin Yao escreveu:
> > > Currently if we run 'perf record -e cycles:u', exclude_guest=0.
> > >
> > > But it doesn't make sense in most cases that we request for
> > > user-space counting but we also get the guest report.
> > >
> > > Of course, we also need to consider perf kvm usage case that
> > > authorized perf users on the host may only want to count guest
> > > user space events. For example,
> > >
> > > perf kvm --guest record -e cycles:u
> > Ok, probably this works, but what if I want to record guest user samples
> > without using 'perf kvm'?
> >
> > Can we have a 'U' modifier, perhaps, for that?
> >
> > I.e.
> >
> > perf record -e cycles:uU would not set exclude_host not exclude_guest,
> > cycles:u excludes guest user, cycles:U excludes host user, would that be
> > possible?
> >
> > Anyway, I think that with what we have, your patch makes sense, having a
> > way to, without using 'perf kvm' still be able to sample the guest can
> > be done on top. of this.
> >
> > Xu, can we get your Reviewed-by if this addresses your concerns?

My concern is about do not break the perf kvm usages and Yao did it in v3.

Tested-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>

> > - Arnaldo
>
> Do you suggest we will create a new modifier 'U' as a follow-up patch?
>
> cycles:u - Count host user space but it doesn't count the guest user space 
> (exclude_host = 0, exclude_guest = 1, exclude_kernel = 1, exclude_user = 0, 
> exclude_hv = 1)
>
> cycles:U - Count the guest user space but it doesn't count the host user 
> space (exclude_host = 1, exclude_guest = 0, exclude_kernel = 1, 
> exclude_user = 0, exclude_hv = 1)
>
> Is above understanding correct?

Do we really need to support sample guests without using perf kvm?

If it's true, I would prefer "cycles:uG" to cover guest user space
events only, "cycles:kG" to cover guest kernel space events only,
and only host events are sampled without the ":G" modifier by default.

I am not sure if ":G" has been used in perf.

At the very least, this v3 patch may not
block the follow-up patch from Yao (if any).

Thanks,
Like Xu

> Thanks
> Jin Yao