linux-kernel - [PATCH] cpufreq: conservative: Take limits changes into account properly

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Date:   Mon, 15 Oct 2018 23:21:05 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux PM <linux-pm@...r.kernel.org>
Cc:     Waldemar Rymarkiewicz <waldemar.rymarkiewicz@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Waldemar Rymarkiewicz <waldemarx.rymarkiewicz@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        t.bartholomae@...el.com
Subject: [PATCH] cpufreq: conservative: Take limits changes into account properly

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

If the policy limits change between invocations of cs_dbs_update(),
the requested frequency value stored in dbs_info may not be updated
and the function may use a stale value of it next time.  Moreover, if
idle periods are takem into account by cs_dbs_update(), the requested
frequency value stored in dbs_info may be below the min policy limit,
which is incorrect.

To fix these problems, always update the requested frequency value
in dbs_info along with the local copy of it when the previous
requested frequency is beyond the policy limits and avoid decreasing
the requested frequency below the min policy limit when taking
idle periods into account.

Reported-by: Waldemar Rymarkiewicz <waldemarx.rymarkiewicz@...el.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpufreq/cpufreq_conservative.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-pm/drivers/cpufreq/cpufreq_conservative.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq_conservative.c
+++ linux-pm/drivers/cpufreq/cpufreq_conservative.c
@@ -80,8 +80,10 @@ static unsigned int cs_dbs_update(struct
 	 * changed in the meantime, so fall back to current frequency in that
 	 * case.
 	 */
-	if (requested_freq > policy->max || requested_freq < policy->min)
+	if (requested_freq > policy->max || requested_freq < policy->min) {
 		requested_freq = policy->cur;
+		dbs_info->requested_freq = requested_freq;
+	}
 
 	freq_step = get_freq_step(cs_tuners, policy);
 
@@ -92,7 +94,7 @@ static unsigned int cs_dbs_update(struct
 	if (policy_dbs->idle_periods < UINT_MAX) {
 		unsigned int freq_steps = policy_dbs->idle_periods * freq_step;
 
-		if (requested_freq > freq_steps)
+		if (requested_freq > policy->min + freq_steps)
 			requested_freq -= freq_steps;
 		else
 			requested_freq = policy->min;