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

[Song Liu]

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?

Thanks,
Song