linux-kernel - [RFC PATCH 7/7] cpufreq: Change default transition delay to 2ms

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230827233203.1315953-8-qyousef@layalina.io>
Date:   Mon, 28 Aug 2023 00:32:03 +0100
From:   Qais Yousef <qyousef@...alina.io>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Lukasz Luba <lukasz.luba@....com>,
        Qais Yousef <qyousef@...alina.io>
Subject: [RFC PATCH 7/7] cpufreq: Change default transition delay to 2ms

10ms is too high for today's hardware, even low end ones. This default
end up being used a lot on Arm machines at least. Pine64, mac mini and
pixel 6 all end up with 10ms rate_limit_us when using schedutil, and
it's too high for all of them.

Change the default to 2ms which should be 'pessimistic' enough for worst
case scenario, but not too high for platforms with fast DVFS hardware.

Signed-off-by: Qais Yousef (Google) <qyousef@...alina.io>
---
 drivers/cpufreq/cpufreq.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 50bbc969ffe5..d8fc33b7f2d2 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -579,11 +579,11 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy)
 		 * for platforms where transition_latency is in milliseconds, it
 		 * ends up giving unrealistic values.
 		 *
-		 * Cap the default transition delay to 10 ms, which seems to be
+		 * Cap the default transition delay to 2 ms, which seems to be
 		 * a reasonable amount of time after which we should reevaluate
 		 * the frequency.
 		 */
-		return min(latency * LATENCY_MULTIPLIER, (unsigned int)10000);
+		return min(latency * LATENCY_MULTIPLIER, (unsigned int)(2*MSEC_PER_SEC));
 	}
 
 	return LATENCY_MULTIPLIER;
-- 
2.34.1