Received-SPF: pass (google.com: domain of linux-kernel+bounces-137908-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Wed, 10 Apr 2024 04:57:45 -0000
From: "tip-bot2 for Namhyung Kim" <tip-bot2@linutronix.de>
Sender: tip-bot2@linutronix.de
Reply-to: linux-kernel@vger.kernel.org
To: linux-tip-commits@vger.kernel.org
Subject: [tip: perf/core] perf/core: Reduce PMU access to adjust sample freq
Cc: Namhyung Kim <namhyung@kernel.org>, Ingo Molnar <mingo@kernel.org>,
 Ian Rogers <irogers@google.com>, Kan Liang <kan.liang@linux.intel.com>,
 x86@kernel.org, linux-kernel@vger.kernel.org
In-Reply-To: <20240207050545.2727923-2-namhyung@kernel.org>
References: <20240207050545.2727923-2-namhyung@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Message-ID: <171272506512.10875.6886742044570226022.tip-bot2@tip-bot2>
Robot-ID: <tip-bot2@linutronix.de>
Robot-Unsubscribe:
 Contact <mailto:tglx@linutronix.de> to get blacklisted from these emails
Precedence: bulk
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit

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

Commit-ID:     f38628b06c36222367e26820879789ae59e49f60
Gitweb:        https://git.kernel.org/tip/f38628b06c36222367e26820879789ae59e49f60
Author:        Namhyung Kim <namhyung@kernel.org>
AuthorDate:    Tue, 06 Feb 2024 21:05:45 -08:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 10 Apr 2024 06:13:57 +02:00

perf/core: Reduce PMU access to adjust sample freq

In perf_adjust_freq_unthr_context(), it first starts the event and then
stop unnecessarily to adjust the sampling frequency if the event is
throttled.

For a throttled non-frequency event, it doesn't have a freq so no need
to adjust.  Just starting the event would be ok.

For a frequency event, whether it's throttled or not, it needs to stop
before adjusting the frequency.  That means it should not start the
even if it was throttled.  I tried to skip calling the stop callback,
but it didn't work well since the event count might not be up to date.
It should call the stop callback with PERF_EF_UPDATE anyway.

However not calling start would prevent unnecessary MSR accesses (which
can be costly) for already stopped events as stop state is saved in the
hw config.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20240207050545.2727923-2-namhyung@kernel.org
---
 kernel/events/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9566cfb..fd94e45 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4146,7 +4146,8 @@ static void perf_adjust_freq_unthr_events(struct list_head *event_list)
 		if (hwc->interrupts == MAX_INTERRUPTS) {
 			hwc->interrupts = 0;
 			perf_log_throttle(event, 1);
-			event->pmu->start(event, 0);
+			if (!event->attr.freq || !event->attr.sample_freq)
+				event->pmu->start(event, 0);
 		}
 
 		if (!event->attr.freq || !event->attr.sample_freq)