cpufreq: Make drivers using CPUFREQ_ETERNAL specify transition latency

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.

Rafael J. Wysocki committed 1 year ago

Commit f97aef01 parent d3f8f8d9 files · +14 −10Browse files

Unified · Split

9 files

drivers/cpufreq/cpufreq-dt.c +1 −1
drivers/cpufreq/imx6q-cpufreq.c +1 −1
drivers/cpufreq/mediatek-cpufreq-hw.c +1 −1
drivers/cpufreq/rcpufreq_dt.rs +1 −1
drivers/cpufreq/scmi-cpufreq.c +1 −1
drivers/cpufreq/scpi-cpufreq.c +1 −1
drivers/cpufreq/spear-cpufreq.c +1 −1
include/linux/cpufreq.h +3 −0
rust/kernel/cpufreq.rs +4 −3

drivers/cpufreq/cpufreq-dt.c+1−1

@@ -104,7 +104,7 @@ static int cpufreq_init(struct cpufreq_policy *policy) · 103 unmodified lines
104	104
105	105	transition_latency = dev_pm_opp_get_max_transition_latency(cpu_dev);
106	106	if (!transition_latency)
107		− transition_latency = CPUFREQ_ETERNAL;
	107	+ transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
108	108
109	109	cpumask_copy(policy->cpus, priv->cpus);
110	110	policy->driver_data = priv;

drivers/cpufreq/imx6q-cpufreq.c+1−1

@@ -442,7 +442,7 @@ soc_opp_out: · 441 unmodified lines
442	442	}
443	443
444	444	if (of_property_read_u32(np, "clock-latency", &transition_latency))
445		− transition_latency = CPUFREQ_ETERNAL;
	445	+ transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
446	446
447	447	/*
448	448	* Calculate the ramp time for max voltage change in the

drivers/cpufreq/mediatek-cpufreq-hw.c+1−1

@@ -309,7 +309,7 @@ static int mtk_cpufreq_hw_cpu_init(struct cpufreq_policy *policy) · 308 unmodified lines
309	309
310	310	latency = readl_relaxed(data->reg_bases[REG_FREQ_LATENCY]) * 1000;
311	311	if (!latency)
312		− latency = CPUFREQ_ETERNAL;
	312	+ latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
313	313
314	314	policy->cpuinfo.transition_latency = latency;
315	315	policy->fast_switch_possible = true;

drivers/cpufreq/rcpufreq_dt.rs+1−1

@@ -123,7 +123,7 @@ impl cpufreq::Driver for CPUFreqDTDriver { · 122 unmodified lines
123	123
124	124	let mut transition_latency = opp_table.max_transition_latency_ns() as u32;
125	125	if transition_latency == 0 {
126		− transition_latency = cpufreq::ETERNAL_LATENCY_NS;
	126	+ transition_latency = cpufreq::DEFAULT_TRANSITION_LATENCY_NS;
127	127	}
128	128
129	129	policy

drivers/cpufreq/scmi-cpufreq.c+1−1

@@ -294,7 +294,7 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy) · 293 unmodified lines
294	294
295	295	latency = perf_ops->transition_latency_get(ph, domain);
296	296	if (!latency)
297		− latency = CPUFREQ_ETERNAL;
	297	+ latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
298	298
299	299	policy->cpuinfo.transition_latency = latency;
300	300

drivers/cpufreq/scpi-cpufreq.c+1−1

@@ -157,7 +157,7 @@ static int scpi_cpufreq_init(struct cpufreq_policy *policy) · 156 unmodified lines
157	157
158	158	latency = scpi_ops->get_transition_latency(cpu_dev);
159	159	if (!latency)
160		− latency = CPUFREQ_ETERNAL;
	160	+ latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
161	161
162	162	policy->cpuinfo.transition_latency = latency;
163	163

drivers/cpufreq/spear-cpufreq.c+1−1

@@ -182,7 +182,7 @@ static int spear_cpufreq_probe(struct platform_device *pdev) · 181 unmodified lines
182	182
183	183	if (of_property_read_u32(np, "clock-latency",
184	184	&spear_cpufreq.transition_latency))
185		− spear_cpufreq.transition_latency = CPUFREQ_ETERNAL;
	185	+ spear_cpufreq.transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
186	186
187	187	cnt = of_property_count_u32_elems(np, "cpufreq_tbl");
188	188	if (cnt <= 0) {

include/linux/cpufreq.h+3−0

@@ -32,6 +32,9 @@ · 31 unmodified lines
32	32	*/
33	33
34	34	#define CPUFREQ_ETERNAL (-1)
	35	+
	36	+#define CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS NSEC_PER_MSEC
	37	+
35	38	#define CPUFREQ_NAME_LEN 16
36	39	/* Print length for names. Extra 1 space for accommodating '\n' in prints */
37	40	#define CPUFREQ_NAME_PLEN (CPUFREQ_NAME_LEN + 1)

rust/kernel/cpufreq.rs+4−3

@@ -39,7 +39,8 @@ use macros::vtable; · 38 unmodified lines
39	39	const CPUFREQ_NAME_LEN: usize = bindings::CPUFREQ_NAME_LEN as usize;
40	40
41	41	/// Default transition latency value in nanoseconds.
42		−pub const ETERNAL_LATENCY_NS: u32 = bindings::CPUFREQ_ETERNAL as u32;
	42	+pub const DEFAULT_TRANSITION_LATENCY_NS: u32 =
	43	+ bindings::CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
43	44
44	45	/// CPU frequency driver flags.
45	46	pub mod flags {
@@ -400,13 +401,13 @@ impl TableBuilder { · 354 unmodified lines
400	401	/// The following example demonstrates how to create a CPU frequency table.
401	402	///
402	403	/// ```
403		−/// use kernel::cpufreq::{ETERNAL_LATENCY_NS, Policy};
	404	+/// use kernel::cpufreq::{DEFAULT_TRANSITION_LATENCY_NS, Policy};
404	405	///
405	406	/// fn update_policy(policy: &mut Policy) {
406	407	/// policy
407	408	/// .set_dvfs_possible_from_any_cpu(true)
408	409	/// .set_fast_switch_possible(true)
409		−/// .set_transition_latency_ns(ETERNAL_LATENCY_NS);
	410	+/// .set_transition_latency_ns(DEFAULT_TRANSITION_LATENCY_NS);
410	411	///
411	412	/// pr_info!("The policy details are: {:?}\n", (policy.cpu(), policy.cur()));
412	413	/// }