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

From: Liang, Kan
Date: Wed Oct 24 2018 - 14:13:00 EST

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))

Thanks. I'll add the nr_mmap_events check in V2.