Re: [PATCH v2 2/2] cpufreq: fix schedutil not returning to non-boost freq when boost is disabled
From: Zhongqiu Han
Date: Tue Sep 22 2026 - 09:53:32 EST
Hi Ananthu,
On 9/21/2026 6:34 PM, Ananthu C V wrote:
Hi Zhongqiu,
On Fri, Sep 18, 2026 at 05:15:07PM +0800, Zhongqiu Han wrote:
Hi Ananthu,
On 9/8/2026 4:30 PM, Ananthu C V wrote:
Commit 538b0188da46 ("cpufreq: ACPI: Set cpuinfo.max_freq directly if
max boost is known") introduced a guard for cpuinfo max updates to only
increase, to preserve driver-set values above the freq table maximum,
causing cpuinfo max to be stuck at boost frequency even when boost is
disabled.
Unconditionally track the highest non-boost frequency (max_base_freq)
in the freq table. When a freq table is available, use max_table_freq/
max_base_freq instead of cpuinfo->max_freq to control boost values, so
the value can decrease again when boost is disabled.
This issue does not appear to be limited to schedutil, so the subject
seems too restrictive.
That makes sense, I'll update it on the next run.
Fixes: 538b0188da46 ("cpufreq: ACPI: Set cpuinfo.max_freq directly if max boost is known")
I already commented on the Fixes: tag in v1.
https://lore.kernel.org/all/3a20b69e-b072-4723-925f-514d8162e259@xxxxxxxxxxxxxxxx/#t
IMO it should be: 6e39ba4e5a82 ("cpufreq: Add boost_freq_req QoS
request")
Could you please comment on this?
The specific issue we are trying to fix is that once boost is disabled the
frequency is not able to come down to a non boost value, which was introduced
by the upward guard added in 538b0188da46. Consequently, if that guard is removed,
the issue does not exist. So it makes sense to add a fixes for that specific
commit.
I just did some testing with the SCMI driver on the SM8850 platform, and
the results matched my previous v1 comments[1]:
02/15/2021 538b0188da46 ("cpufreq: ACPI: Set cpuinfo.max_freq directly
if max boost is known") ---> Not reproduced
03/26/2026 6e39ba4e5a82 ("cpufreq: Add boost_freq_req QoS request")
---> Not reproduced
03/28/2026 db80ad776cd2 ("cpufreq: Remove driver default policy->min
/max init") ---> Reproduced the issue
[1]: https://lore.kernel.org/all/3a20b69e-b072-4723-925f-514d8162e259@xxxxxxxxxxxxxxxx/#t
538b0188da46 made cpuinfo.max_freq increase-only, so it stays pinned at
the boost frequency once boost has been enabled. This stayed harmless
because cpufreq_frequency_table_cpuinfo() also assigned policy->max =
max_freq; directly, recomputed per boost state on every call.
6e39ba4e5a82 moved the boost QoS update to the dirty cpuinfo.max_freq,
but since that value is unchanged on disable, freq_qos_update_request()
bails out early, cpufreq_set_policy() is never invoked and the directly
written policy->max survives, so the bug remained invisible.
db80ad776cd2 then deleted policy->max = max_freq;, leaving nothing to
bring policy->max back down from the boost value that
cpufreq_set_policy() had installed when boost was enabled.
Correcting myself: from the point of view of where the issue first
becomes reproducible, the Fixes tag can be:
Fixes: db80ad776cd2 ("cpufreq: Remove driver default policy->min/max
init")
Comments are welcome.
Signed-off-by: Ananthu C V <ananthu.cv@xxxxxxxxxxxxxxxx>
---
drivers/cpufreq/cpufreq.c | 14 +++++++++++++-
drivers/cpufreq/freq_table.c | 5 +++++
include/linux/cpufreq.h | 1 +
3 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 0d0df986fa3d..a13e72711597 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -574,6 +574,7 @@ static ssize_t show_local_boost(struct cpufreq_policy *policy, char *buf)
static int policy_set_boost(struct cpufreq_policy *policy, bool enable)
{
+ unsigned int max_freq;
int ret;
if (policy->boost_enabled == enable)
@@ -587,7 +588,18 @@ static int policy_set_boost(struct cpufreq_policy *policy, bool enable)
return ret;
}
- ret = freq_qos_update_request(&policy->boost_freq_req, policy->cpuinfo.max_freq);
+ if (policy->freq_table) {
acpi-cpufreq has a freq table but never sets CPUFREQ_BOOST_FREQ, so
max_table_freq == max_base_freq == _PSS P0 here, and the real boost
ceiling kept in cpuinfo.max_freq is lost. It seems that the condition
needs to be "does the freq table list boost frequencies" rather than "is
there a freq table" — e.g. recorded during the table scan, the same way
boost_supported is derived from the flags in
cpufreq_table_validate_and_sort(). And then:
if (policy->cpuinfo.boost_in_table) {
xxx;
}
That makes sense. I think the best thing to do here will be to export/move
policy_has_boost_freq from freq_table.c and reuse it. Comments on this are
welcome.
+ max_freq = enable ? policy->cpuinfo.max_table_freq :
+ policy->cpuinfo.max_base_freq;
+
+ if (!max_freq)
+ /* when the freq table contains only boost frequencies */
+ max_freq = policy->cpuinfo.max_table_freq;
+ } else {
+ max_freq = policy->cpuinfo.max_freq;
+ }
+
+ ret = freq_qos_update_request(&policy->boost_freq_req, max_freq);
if (ret < 0) {
policy->boost_enabled = !policy->boost_enabled;
cpufreq_driver->set_boost(policy, policy->boost_enabled);
diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
index 4984142dc08a..7e183e16162d 100644
--- a/drivers/cpufreq/freq_table.c
+++ b/drivers/cpufreq/freq_table.c
@@ -34,6 +34,7 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
unsigned int min_freq = ~0;
unsigned int max_freq = 0;
unsigned int max_table_freq = 0;
+ unsigned int max_base_freq = 0;
unsigned int freq, i;
cpufreq_for_each_valid_entry_idx(pos, table, i) {
@@ -42,6 +43,9 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
if (freq > max_table_freq)
max_table_freq = freq;
+ if (!(pos->flags & CPUFREQ_BOOST_FREQ) && freq > max_base_freq)
+ max_base_freq = freq;
+
if ((!cpufreq_boost_enabled() || !policy->boost_enabled)
&& (pos->flags & CPUFREQ_BOOST_FREQ))
continue;
@@ -62,6 +66,7 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
policy->cpuinfo.max_freq = max_freq;
policy->cpuinfo.max_table_freq = max_table_freq;
+ policy->cpuinfo.max_base_freq = max_base_freq;
if (min_freq == ~0)
return -EINVAL;
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 3f3b1380251a..419c71ccff7c 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -46,6 +46,7 @@ struct cpufreq_cpuinfo {
unsigned int max_freq;
unsigned int min_freq;
unsigned int max_table_freq; /* Highest valid frequency in the table */
+ unsigned int max_base_freq; /* Highest non-boost frequency in the table */
/* in 10^(-9) s = nanoseconds */
unsigned int transition_latency;
--
Thx and BRs,
Zhongqiu Han
Best,
Ananthu
--
Thx and BRs,
Zhongqiu Han