lkml.org 
[lkml]   [2022]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [RFC v2] perf: Rewrite core context handling
From
On 22-Aug-22 10:14 PM, Peter Zijlstra wrote:
> On Tue, Aug 02, 2022 at 11:40:34AM +0530, Ravi Bangoria wrote:
>> On 13-Jun-22 8:25 PM, Peter Zijlstra wrote:
>>> On Mon, Jun 13, 2022 at 04:35:11PM +0200, Peter Zijlstra wrote:
>>>> @@ -12125,6 +12232,8 @@ SYSCALL_DEFINE5(perf_event_open,
>>>> goto err_task;
>>>> }
>>>>
>>>> + // XXX premature; what if this is allowed, but we get moved to a PMU
>>>> + // that doesn't have this.
>>>> if (is_sampling_event(event)) {
>>>> if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
>>>> err = -EOPNOTSUPP;
>>>
>>> No; this really should be against the event's native PMU. If the event
>>> can't natively sample, it can't sample when placed in another group
>>> either.
>>
>> Right. But IIUC, the question was, would there be any issue if we allow
>> grouping of perf_sw_context sampling event as group leader and
>> perf_{hw|invalid}_context counting event as group member. I think no. It
>> should just work fine. And, there could be real usecases of it as you
>> described in one old thread[1].
>
> Like you I need to bend my brain around this again, but I'm not seeing a
> contradiction. The use-case from [1] is a software sampler with a bunch
> of non-sampling uncore events.
>
> The uncore events aren't sampling, the are simply read by the software
> event (SAMPLE_READ). And moving the sampling software event to the
> non-sample capable uncore PMU shouldn't matter.

Ok.

> That is; the code as it stands here seems right, we should check
> is_sampling_event() against an event's native pmu->capabilities.
>
> Or am I misunderstanding things?

No, that's correct. We must use event's native pmu to check capabilities.
I'll remove this comment from code.

Thanks,
Ravi

\
 
 \ /
  Last update: 2022-08-23 06:49    [W:0.158 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site