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

[Peter Zijlstra]

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);


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