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From: "Liang, Kan" <kan.liang@intel.com>
To: Peter Zijlstra <peterz@infradead.org>, Song Liu <songliubraving@fb.com>
Cc: Like Xu <like.xu.linux@gmail.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Kernel Team <Kernel-team@fb.com>,
	Andrii Nakryiko <andrii@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	"like.xu@linux.intel.com" <like.xu@linux.intel.com>,
	Andi Kleen <andi@firstfloor.org>
Subject: RE: bpf_get_branch_snapshot on qemu-kvm
Date: Wed, 29 Sep 2021 16:35:35 +0000	[thread overview]
Message-ID: <SJ0PR11MB4814BBE6651FB9F8F05868FBE8A99@SJ0PR11MB4814.namprd11.prod.outlook.com> (raw)
In-Reply-To: <YVSNV/1tFRGWIa6c@hirez.programming.kicks-ass.net>

> > > - get confirmation that clearing GLOBAL_CTRL is suffient to supress
> > >   PEBS, in which case we can simply remove the PEBS_ENABLE clear.
> >
> > How should we confirm this? Can we run some tests for this? Or do we
> > need hardware experts' input for this?
> 
> I'll put it on the list to ask the hardware people when I talk to them next. But
> maybe Kan or Andi know without asking.

If the GLOBAL_CTRL is explicitly disabled, the counters do not count anymore.
It doesn't matter if PEBS is enabled or not. 

See 6c1c07b33eb0 ("perf/x86/intel: Avoid unnecessary PEBS_ENABLE MSR
access in PMI "). We optimized the PMU handler base on it.

Thanks,
Kan

  reply	other threads:[~2021-09-29 16:35 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29  0:04 bpf_get_branch_snapshot on qemu-kvm Song Liu
2021-09-29  7:35 ` Peter Zijlstra
2021-09-29 12:05   ` Like Xu
2021-09-29 12:26     ` Peter Zijlstra
2021-09-29 14:42       ` Song Liu
2021-09-29 15:59         ` Peter Zijlstra
2021-09-29 16:35           ` Liang, Kan [this message]
2021-09-29 20:05             ` Song Liu
2021-10-08  3:34               ` Like Xu
2021-10-08  5:46                 ` Song Liu
2021-10-08  6:36                   ` Like Xu
2021-10-08 17:08                     ` Song Liu
2021-10-09  9:03                       ` Like Xu
2021-10-26  7:09                         ` Song Liu
2021-10-28  3:09                           ` Like Xu
2021-10-29 18:09                             ` Song Liu
2021-09-29 23:20           ` Andi Kleen
2021-09-29 14:39     ` Song Liu

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