Re: [RFC PATCH v3 10/58] perf: Add generic exclude_guest support

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Thu, Aug 01, 2024 at 04:58:19AM +0000, Mingwei Zhang wrote:
> +void perf_guest_exit(void)
> +{
> +	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
> +
> +	lockdep_assert_irqs_disabled();
> +
> +	perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> +
> +	if (WARN_ON_ONCE(!__this_cpu_read(perf_in_guest)))
> +		goto unlock;
> +
> +	perf_ctx_disable(&cpuctx->ctx, EVENT_GUEST);
> +	ctx_sched_in(&cpuctx->ctx, EVENT_GUEST);
> +	perf_ctx_enable(&cpuctx->ctx, EVENT_GUEST);
> +	if (cpuctx->task_ctx) {
> +		perf_ctx_disable(cpuctx->task_ctx, EVENT_GUEST);
> +		ctx_sched_in(cpuctx->task_ctx, EVENT_GUEST);
> +		perf_ctx_enable(cpuctx->task_ctx, EVENT_GUEST);
> +	}

Does this not violate the scheduling order of events? AFAICT this will
do:

  cpu pinned
  cpu flexible
  task pinned
  task flexible

as opposed to:

  cpu pinned
  task pinned
  cpu flexible
  task flexible

We have the perf_event_sched_in() helper for this.

> +
> +	__this_cpu_write(perf_in_guest, false);
> +unlock:
> +	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> +}
> +EXPORT_SYMBOL_GPL(perf_guest_exit);