linux-kernel - Re: [RFC PATCH 02/41] perf: Support guest enter/exit interfaces

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Date: Wed, 20 Mar 2024 09:40:31 -0700
From: Raghavendra Rao Ananta <rananta@...gle.com>
To: Xiong Zhang <xiong.y.zhang@...ux.intel.com>
Cc: seanjc@...gle.com, pbonzini@...hat.com, peterz@...radead.org, 
	mizhang@...gle.com, kan.liang@...el.com, zhenyuw@...ux.intel.com, 
	dapeng1.mi@...ux.intel.com, jmattson@...gle.com, kvm@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	zhiyuan.lv@...el.com, eranian@...gle.com, irogers@...gle.com, 
	samantha.alt@...el.com, like.xu.linux@...il.com, chao.gao@...el.com, 
	Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [RFC PATCH 02/41] perf: Support guest enter/exit interfaces

Hi Kan,

>
> +static void __perf_force_exclude_guest_pmu(struct perf_event_pmu_context *pmu_ctx,
> +                                          struct perf_event *event)
> +{
> +       struct perf_event_context *ctx = pmu_ctx->ctx;
> +       struct perf_event *sibling;
> +       bool include_guest = false;
> +
> +       event_sched_out(event, ctx);
> +       if (!event->attr.exclude_guest)
> +               include_guest = true;
> +       for_each_sibling_event(sibling, event) {
> +               event_sched_out(sibling, ctx);
> +               if (!sibling->attr.exclude_guest)
> +                       include_guest = true;
> +       }
> +       if (include_guest) {
> +               perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
> +               for_each_sibling_event(sibling, event)
> +                       perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
> +       }
Does the perf core revert the PERF_EVENT_STATE_ERROR state somewhere
from the perf_guest_exit() path, or is it expected to remain in this
state?
IIUC, in the perf_guest_exit() path, when we land into
merge_sched_in(), we never schedule the event back if event->state <=
PERF_EVENT_STATE_OFF.

Thank you.
Raghavendra