linux-kernel - Re: [RFC v2] perf: Rewrite core context handling

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Message-ID: <YwX546d8YxRCbQWl@worktop.programming.kicks-ass.net>
Date:   Wed, 24 Aug 2022 12:13:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, songliubraving@...com,
        eranian@...gle.com, alexey.budankov@...ux.intel.com,
        ak@...ux.intel.com, mark.rutland@....com, megha.dey@...el.com,
        frederic@...nel.org, maddy@...ux.ibm.com, irogers@...gle.com,
        kim.phillips@....com, linux-kernel@...r.kernel.org,
        santosh.shukla@....com
Subject: Re: [RFC v2] perf: Rewrite core context handling

On Fri, Jun 17, 2022 at 03:36:51PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 13, 2022 at 04:35:11PM +0200, Peter Zijlstra wrote:
> > +/* XXX: No need of list now. Convert it to per-cpu variable */
> >  static DEFINE_PER_CPU(struct list_head, cgrp_cpuctx_list);
> 
> Something like so I suppose...
> 

I need this on top to avoid a spat on perf_cgroup_attach()

---


diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0cd81a3ef374..c6b64a48dea6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -13536,9 +13536,12 @@ static int perf_cgroup_css_online(struct cgroup_subsys_state *css)
 static int __perf_cgroup_move(void *info)
 {
 	struct task_struct *task = info;
-	rcu_read_lock();
-	perf_cgroup_switch(task);
-	rcu_read_unlock();
+
+	preempt_disable();
+	if (atomic_read(this_cpu_ptr(&perf_cgroup_events)))
+		perf_cgroup_switch(task);
+	preempt_enable();
+
 	return 0;
 }