Re: [PATCH v2 2/4] perf/core: Provide a kernel-internal interface to pause perf_event

[Like Xu]

On 2019/10/14 19:51, Peter Zijlstra wrote:
> On Sun, Oct 13, 2019 at 05:15:31PM +0800, Like Xu wrote:
> > Exporting perf_event_pause() as an external accessor for kernel users (such
> > as KVM) who may do both disable perf_event and read count with just one
> > time to hold perf_event_ctx_lock. Also the value could be reset optionally.
>
> > +u64 perf_event_pause(struct perf_event *event, bool reset)
> > +{
> > +	struct perf_event_context *ctx;
> > +	u64 count, enabled, running;
> > +
> > +	ctx = perf_event_ctx_lock(event);
>
> > +	_perf_event_disable(event);
> > +	count = __perf_event_read_value(event, &enabled, &running);
> > +	if (reset)
> > +		local64_set(&event->count, 0);
>
> This local64_set() already assumes there are no child events, so maybe
> write the thing like:
>
> 	WARN_ON_ONCE(event->attr.inherit);
> 	_perf_event_disable(event);
> 	count = local64_read(&event->count);
> 	local64_set(&event->count, 0);

Thanks. It looks good to me and I will apply this.

> > +	perf_event_ctx_unlock(event, ctx);
> > +
> > +	return count;
> > +}
> > +EXPORT_SYMBOL_GPL(perf_event_pause);