| 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
| ||
|
Message-ID: <aNiqTYZai83Yguqt@dragon>
Date: Sun, 28 Sep 2025 11:23:57 +0800
From: Shawn Guo <shawnguo2@...h.net>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Linux PM <linux-pm@...r.kernel.org>, Shawn Guo <shawnguo@...nel.org>,
Qais Yousef <qyousef@...alina.io>,
LKML <linux-kernel@...r.kernel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Pierre Gondois <pierre.gondois@....com>,
Mario Limonciello <mario.limonciello@....com>,
Linux ACPI <linux-acpi@...r.kernel.org>,
Jie Zhan <zhanjie9@...ilicon.com>, rust-for-linux@...r.kernel.org,
Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>
Subject: Re: [PATCH v3 1/4] cpufreq: Make drivers using CPUFREQ_ETERNAL
specify transition latency
On Fri, Sep 26, 2025 at 12:12:37PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Commit a755d0e2d41b ("cpufreq: Honour transition_latency over
> transition_delay_us") caused platforms where cpuinfo.transition_latency
> is CPUFREQ_ETERNAL to get a very large transition latency whereas
> previously it had been capped at 10 ms (and later at 2 ms).
>
> This led to a user-observable regression between 6.6 and 6.12 as
> described by Shawn:
>
> "The dbs sampling_rate was 10000 us on 6.6 and suddently becomes
> 6442450 us (4294967295 / 1000 * 1.5) on 6.12 for these platforms
> because the default transition delay was dropped [...].
>
> It slows down dbs governor's reacting to CPU loading change
> dramatically. Also, as transition_delay_us is used by schedutil
> governor as rate_limit_us, it shows a negative impact on device
> idle power consumption, because the device gets slightly less time
> in the lowest OPP."
>
> Evidently, the expectation of the drivers using CPUFREQ_ETERNAL as
> cpuinfo.transition_latency was that it would be capped by the core,
> but they may as well return a default transition latency value instead
> of CPUFREQ_ETERNAL and the core need not do anything with it.
>
> Accordingly, introduce CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS and make
> all of the drivers in question use it instead of CPUFREQ_ETERNAL. Also
> update the related Rust binding.
>
> Fixes: a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us")
> Closes: https://lore.kernel.org/linux-pm/20250922125929.453444-1-shawnguo2@yeah.net/
> Reported-by: Shawn Guo <shawnguo@...nel.org>
> Reviewed-by: Mario Limonciello (AMD) <superm1@...nel.org>
> Reviewed-by: Jie Zhan <zhanjie9@...ilicon.com>
> Cc: 6.6+ <stable@...r.kernel.org> # 6.6+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>
> v1 -> v3:
> * Add updates of the Rust version of cpufreq-dt and Rust binding
> * Update the changelog
> * Add tags from Mario Limonciello and Jie Zhan
>
> ---
> drivers/cpufreq/cpufreq-dt.c | 2 +-
> drivers/cpufreq/imx6q-cpufreq.c | 2 +-
> drivers/cpufreq/mediatek-cpufreq-hw.c | 2 +-
> drivers/cpufreq/rcpufreq_dt.rs | 2 +-
> drivers/cpufreq/scmi-cpufreq.c | 2 +-
> drivers/cpufreq/scpi-cpufreq.c | 2 +-
> drivers/cpufreq/spear-cpufreq.c | 2 +-
> include/linux/cpufreq.h | 3 +++
> rust/kernel/cpufreq.rs | 7 ++++---
> 9 files changed, 14 insertions(+), 10 deletions(-)
>
> --- a/drivers/cpufreq/cpufreq-dt.c
> +++ b/drivers/cpufreq/cpufreq-dt.c
> @@ -104,7 +104,7 @@ static int cpufreq_init(struct cpufreq_p
>
> transition_latency = dev_pm_opp_get_max_transition_latency(cpu_dev);
> if (!transition_latency)
> - transition_latency = CPUFREQ_ETERNAL;
> + transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> cpumask_copy(policy->cpus, priv->cpus);
> policy->driver_data = priv;
> --- a/drivers/cpufreq/imx6q-cpufreq.c
> +++ b/drivers/cpufreq/imx6q-cpufreq.c
> @@ -442,7 +442,7 @@ soc_opp_out:
> }
>
> if (of_property_read_u32(np, "clock-latency", &transition_latency))
> - transition_latency = CPUFREQ_ETERNAL;
> + transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> /*
> * Calculate the ramp time for max voltage change in the
> --- a/drivers/cpufreq/mediatek-cpufreq-hw.c
> +++ b/drivers/cpufreq/mediatek-cpufreq-hw.c
> @@ -309,7 +309,7 @@ static int mtk_cpufreq_hw_cpu_init(struc
>
> latency = readl_relaxed(data->reg_bases[REG_FREQ_LATENCY]) * 1000;
> if (!latency)
> - latency = CPUFREQ_ETERNAL;
> + latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> policy->cpuinfo.transition_latency = latency;
> policy->fast_switch_possible = true;
> --- a/drivers/cpufreq/rcpufreq_dt.rs
> +++ b/drivers/cpufreq/rcpufreq_dt.rs
> @@ -123,7 +123,7 @@ impl cpufreq::Driver for CPUFreqDTDriver
>
> let mut transition_latency = opp_table.max_transition_latency_ns() as u32;
> if transition_latency == 0 {
> - transition_latency = cpufreq::ETERNAL_LATENCY_NS;
> + transition_latency = cpufreq::DEFAULT_TRANSITION_LATENCY_NS;
> }
>
> policy
> --- a/drivers/cpufreq/scmi-cpufreq.c
> +++ b/drivers/cpufreq/scmi-cpufreq.c
> @@ -294,7 +294,7 @@ static int scmi_cpufreq_init(struct cpuf
>
> latency = perf_ops->transition_latency_get(ph, domain);
> if (!latency)
> - latency = CPUFREQ_ETERNAL;
> + latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> policy->cpuinfo.transition_latency = latency;
>
> --- a/drivers/cpufreq/scpi-cpufreq.c
> +++ b/drivers/cpufreq/scpi-cpufreq.c
> @@ -157,7 +157,7 @@ static int scpi_cpufreq_init(struct cpuf
>
> latency = scpi_ops->get_transition_latency(cpu_dev);
> if (!latency)
> - latency = CPUFREQ_ETERNAL;
> + latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> policy->cpuinfo.transition_latency = latency;
>
> --- a/drivers/cpufreq/spear-cpufreq.c
> +++ b/drivers/cpufreq/spear-cpufreq.c
> @@ -182,7 +182,7 @@ static int spear_cpufreq_probe(struct pl
>
> if (of_property_read_u32(np, "clock-latency",
> &spear_cpufreq.transition_latency))
> - spear_cpufreq.transition_latency = CPUFREQ_ETERNAL;
> + spear_cpufreq.transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
>
> cnt = of_property_count_u32_elems(np, "cpufreq_tbl");
> if (cnt <= 0) {
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -32,6 +32,9 @@
> */
>
> #define CPUFREQ_ETERNAL (-1)
> +
> +#define CPUFREQ_DEFAULT_TANSITION_LATENCY_NS NSEC_PER_MSEC
Typo of TANSITION, should be CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS.
Shawn
> +
> #define CPUFREQ_NAME_LEN 16
> /* Print length for names. Extra 1 space for accommodating '\n' in prints */
> #define CPUFREQ_NAME_PLEN (CPUFREQ_NAME_LEN + 1)
> --- a/rust/kernel/cpufreq.rs
> +++ b/rust/kernel/cpufreq.rs
> @@ -39,7 +39,8 @@ use macros::vtable;
> const CPUFREQ_NAME_LEN: usize = bindings::CPUFREQ_NAME_LEN as usize;
>
> /// Default transition latency value in nanoseconds.
> -pub const ETERNAL_LATENCY_NS: u32 = bindings::CPUFREQ_ETERNAL as u32;
> +pub const DEFAULT_TRANSITION_LATENCY_NS: u32 =
> + bindings::CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS as u32;
>
> /// CPU frequency driver flags.
> pub mod flags {
> @@ -400,13 +401,13 @@ impl TableBuilder {
> /// The following example demonstrates how to create a CPU frequency table.
> ///
> /// ```
> -/// use kernel::cpufreq::{ETERNAL_LATENCY_NS, Policy};
> +/// use kernel::cpufreq::{DEFAULT_TRANSITION_LATENCY_NS, Policy};
> ///
> /// fn update_policy(policy: &mut Policy) {
> /// policy
> /// .set_dvfs_possible_from_any_cpu(true)
> /// .set_fast_switch_possible(true)
> -/// .set_transition_latency_ns(ETERNAL_LATENCY_NS);
> +/// .set_transition_latency_ns(DEFAULT_TRANSITION_LATENCY_NS);
> ///
> /// pr_info!("The policy details are: {:?}\n", (policy.cpu(), policy.cur()));
> /// }
>
>
>
Powered by blists - more mailing lists