Re: [PATCHSET 0/8] perf tools: Do not set attr.exclude_guest by default (v4)

[Namhyung Kim]

On Tue, Oct 01, 2024 at 01:46:36PM -0400, Liang, Kan wrote:
> 
> 
> On 2024-09-30 8:20 p.m., Namhyung Kim wrote:
> > Hello,
> > 
> > I found perf tools set exclude_guest bit inconsistently.  It used to
> > set the bit but now the default event for perf record doesn't.  So I'm
> > wondering why we want the bit in the first place.
> > 
> > Actually it's not good for PMUs don't support any exclusion like AMD
> > IBS because it disables new features after the exclude_guest due to
> > the missing feature detection logic.
> > 
> > v4 changes)
> > 
> >  * handle EOPNOTSUPP error in compatible way  (Kan)
> >  * drop --exclude-guest option in perf stat
> >  * not to separate exclude_hv fallback
> >  * rename to exclude_GH_default  (Kan)
> >  * drop the RFC from the subject
> > 
> > v3) https://lore.kernel.org/lkml/20240905202426.2690105-1-namhyung@xxxxxxxxxx/
> > 
> >  * move exclude_guest fallback to the front
> >  * fix precise_max handling on AMD
> >  * simplify the default event for perf record
> > 
> > v2) https://lore.kernel.org/lkml/20240904064131.2377873-1-namhyung@xxxxxxxxxx/
> > 
> >  * update the missing feature detection logic
> >  * separate exclude_hv fallback
> >  * add new fallback for exclude_guest
> > 
> > v1) https://lore.kernel.org/lkml/20240902014621.2002343-1-namhyung@xxxxxxxxxx/
> > 
> > AFAIK it doesn't matter for the most cases but perf kvm.  If users
> > need to set the bit, they can still use :H modifier.  For vPMU pass-
> > through or Apple M1, it'd add the exclude_guest during the fallback
> > logic.
> > 
> > Also the kernel feature detection logic should be separated from the
> > exclude bit tests since it depends on the PMU implementation rather
> > than the core kernel features.  So I changed it to use a software
> > event for the detection and factor out some hw-specific checks.
> > 
> > The code is available at 'perf/exclude-v4' branch in
> > git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
> > 
> > Thanks,
> > Namhyung
> > 
> > 
> > Namhyung Kim (8):
> >   perf tools: Add fallback for exclude_guest
> >   perf tools: Don't set attr.exclude_guest by default
> >   perf tools: Simplify evsel__add_modifier()
> >   perf tools: Do not set exclude_guest for precise_ip
> >   perf tools: Detect missing kernel features properly
> >   perf tools: Move x86__is_amd_cpu() to util/env.c
> >   perf tools: Check fallback error and order
> >   perf record: Just use "cycles:P" as the default event
> > 
> 
> The patch set looks good to me.
> 
> Acked-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

Thanks for your review!
Namhyung