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Date:   Wed, 24 Oct 2018 11:28:54 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     "Liang, Kan" <kan.liang@linux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        bp@alien8.de, Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 1/2] perf: Add munmap callback
Message-ID: <20181024182854.GH6218@tassilo.jf.intel.com>
References: <20181024151116.30935-1-kan.liang@linux.intel.com>
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 <20181024163208.GC15106@kernel.org>
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> > void perf_event_mmap(struct vm_area_struct *vma)
> > {
> >          struct perf_mmap_event mmap_event;
> > 
> >          if (!atomic_read(&nr_mmap_events))
> >                  return;
> > <SNIP>
> > }
> > 
> 
> Thanks. I'll add the nr_mmap_events check in V2.

No, that's the wrong check here. The PEBS flush is independent of mmap
events being requested.

If anything would need to check for any PEBS events active, which
would need a new counter.  I think the easiest is to just check if 
this_cpu_ptr(&sched_cb_list)
is empty, which should be good enough.

-Andi