linux-kernel - [tip: perf/core] perf: Fix task context PMU for Hetero

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Message-ID: <162451858512.395.11784887696338727719.tip-bot2@tip-bot2>
Date:   Thu, 24 Jun 2021 07:09:45 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Kan Liang <kan.liang@...ux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf: Fix task context PMU for Hetero

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     012669c740e6e2afa8bdb95394d06676f933dd2d
Gitweb:        https://git.kernel.org/tip/012669c740e6e2afa8bdb95394d06676f933dd2d
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Tue, 22 Jun 2021 16:21:01 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 23 Jun 2021 18:30:56 +02:00

perf: Fix task context PMU for Hetero

On HETEROGENEOUS hardware (ARM big.Little, Intel Alderlake etc.) each
CPU might have a different hardware PMU. Since each such PMU is
represented by a different struct pmu, but we only have a single HW
task context.

That means that the task context needs to switch PMU type when it
switches CPUs.

Not doing this means that ctx->pmu calls (pmu_{dis,en}able(),
{start,commit,cancel}_txn() etc.) are called against the wrong PMU and
things will go wobbly.

Fixes: f83d2f91d259 ("perf/x86/intel: Add Alder Lake Hybrid support")
Reported-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Kan Liang <kan.liang@...ux.intel.com>
Link: https://lkml.kernel.org/r/YMsy7BuGT8nBTspT@hirez.programming.kicks-ass.net
---
 kernel/events/core.c |  9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6c964de..0e125ae 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3822,9 +3822,16 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
 					struct task_struct *task)
 {
 	struct perf_cpu_context *cpuctx;
-	struct pmu *pmu = ctx->pmu;
+	struct pmu *pmu;
 
 	cpuctx = __get_cpu_context(ctx);
+
+	/*
+	 * HACK: for HETEROGENEOUS the task context might have switched to a
+	 * different PMU, force (re)set the context,
+	 */
+	pmu = ctx->pmu = cpuctx->ctx.pmu;
+
 	if (cpuctx->task_ctx == ctx) {
 		if (cpuctx->sched_cb_usage)
 			__perf_pmu_sched_task(cpuctx, true);