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Date: Mon, 14 Oct 2024 13:20:43 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mingwei Zhang <mizhang@google.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Xiong Zhang <xiong.y.zhang@intel.com>,
	Dapeng Mi <dapeng1.mi@linux.intel.com>,
	Kan Liang <kan.liang@intel.com>,
	Zhenyu Wang <zhenyuw@linux.intel.com>,
	Manali Shukla <manali.shukla@amd.com>,
	Sandipan Das <sandipan.das@amd.com>,
	Jim Mattson <jmattson@google.com>,
	Stephane Eranian <eranian@google.com>,
	Ian Rogers <irogers@google.com>, Namhyung Kim <namhyung@kernel.org>,
	gce-passthrou-pmu-dev@google.com,
	Samantha Alt <samantha.alt@intel.com>,
	Zhiyuan Lv <zhiyuan.lv@intel.com>, Yanfei Xu <yanfei.xu@intel.com>,
	Like Xu <like.xu.linux@gmail.com>,
	Raghavendra Rao Ananta <rananta@google.com>, kvm@vger.kernel.org,
	linux-perf-users@vger.kernel.org
Subject: Re: [RFC PATCH v3 10/58] perf: Add generic exclude_guest support
Message-ID: <20241014112043.GD16066@noisy.programming.kicks-ass.net>
References: <20240801045907.4010984-1-mizhang@google.com>
 <20240801045907.4010984-11-mizhang@google.com>
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In-Reply-To: <20240801045907.4010984-11-mizhang@google.com>

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);