Re: [PATCH 1/2] perf: Add munmap callback

From: "Liang, Kan" <kan.liang@linux.intel.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>,
	Andi Kleen <ak@linux.intel.com>
Cc: 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
Date: Wed, 24 Oct 2018 14:12:54 -0400	[thread overview]
Message-ID: <18d5fcf4-84b2-806c-eb2c-787b96e0fb90@linux.intel.com> (raw)
In-Reply-To: <20181024163208.GC15106@kernel.org>

On 10/24/2018 12:32 PM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Oct 24, 2018 at 09:23:34AM -0700, Andi Kleen escreveu:
>>> +void perf_event_munmap(void)
>>> +{
>>> +	struct perf_cpu_context *cpuctx;
>>> +	unsigned long flags;
>>> +	struct pmu *pmu;
>>> +
>>> +	local_irq_save(flags);
>>> +	list_for_each_entry(cpuctx, this_cpu_ptr(&sched_cb_list), sched_cb_entry) {
>>
>> Would be good have a fast path here that checks for the list being empty
>> without disabling the interrupts. munmap can be somewhat hot. I think
>> it's ok to make it slower with perf running, but we shouldn't impact
>> it without perf.
> 
> Right, look at how its counterpart, perf_event_mmap() works:
> 
> 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.

Thanks,
Kan