Re: [PATCH v5 bpf-next 1/3] perf: enable branch record for software events

[Peter Zijlstra]

On Fri, Sep 03, 2021 at 04:45:29PM +0000, Song Liu wrote:
> Hi Peter,
> 
> > On Sep 3, 2021, at 1:27 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > 
> > On Thu, Sep 02, 2021 at 09:57:04AM -0700, Song Liu wrote:
> > 
> >> +static int
> >> +intel_pmu_snapshot_branch_stack(struct perf_branch_entry *entries, unsigned int cnt)
> >> +{
> >> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> >> +
> >> +	intel_pmu_disable_all();
> >> +	intel_pmu_lbr_read();
> >> +	cnt = min_t(unsigned int, cnt, x86_pmu.lbr_nr);
> >> +
> >> +	memcpy(entries, cpuc->lbr_entries, sizeof(struct perf_branch_entry) * cnt);
> >> +	intel_pmu_enable_all(0);
> >> +	return cnt;
> >> +}
> > 
> > Given this disables the PMI from 'random' contexts, should we not add
> > IRQ disabling around this to avoid really bad behaviour?
> 
> Do you mean we should add (instead of not add) IRQ disable?

Yeah, I tihnk we want local_irq_save()/restore() here.