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Date: Mon, 4 Mar 2019 16:26:16 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Quentin Perret <quentin.perret@....com>
Cc: Wang, Vincent (王争)
<Vincent.Wang@...soc.com>,
Zhang, Chunyan (张春艳)
<Chunyan.Zhang@...soc.com>, Ingo Molnar <mingo@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Chunyan Zhang <zhang.lyra@...il.com>,
"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: 答复: [PATCH V4] sched/cpufreq: initialize iowait_boost_max and
iowait_boost with cpu capacity
On Mon, Mar 04, 2019 at 01:58:12PM +0000, Quentin Perret wrote:
> You could also update the values in sugov_get_util() at the cost of a
> small overhead to compute 'min'. I'm not sure what's preferable since
> we wanted to avoid that kind of overhead in the first place ...
Or,... we could actually make things simpler.
How's the below? I have a feq questions wrt min, mostly:
- what's the difference between policy->min and
policy->cpuinfo.min_freq; it used to be the former, the below uses
the latter.
- should we have a min_freq based value, instead of a constant; the
difference being that with this the actual boost speed depends in the
gap between min/max.
Anyway; the below converts iowait_boost to capacity scale (from kHz), it
side-steps the whole issue you guys are bickering about by limiting it
to SCHED_CAPACITY_SCALE (aka. 1024) on the boost path, and then limiting
it to @max by the time we figured out we ought to use it.
And since that means we never change @max anymore; we can simplify whole
return value thing.
---
kernel/sched/cpufreq_schedutil.c | 57 ++++++++++++++--------------------------
1 file changed, 20 insertions(+), 37 deletions(-)
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 2efe629425be..d1b8e7aeed44 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -48,10 +48,10 @@ struct sugov_cpu {
bool iowait_boost_pending;
unsigned int iowait_boost;
- unsigned int iowait_boost_max;
u64 last_update;
unsigned long bw_dl;
+ unsigned long min;
unsigned long max;
/* The field below is for single-CPU policies only: */
@@ -303,8 +303,7 @@ static bool sugov_iowait_reset(struct sugov_cpu *sg_cpu, u64 time,
if (delta_ns <= TICK_NSEC)
return false;
- sg_cpu->iowait_boost = set_iowait_boost
- ? sg_cpu->sg_policy->policy->min : 0;
+ sg_cpu->iowait_boost = set_iowait_boost ? sg_cpu->min : 0;
sg_cpu->iowait_boost_pending = set_iowait_boost;
return true;
@@ -344,14 +343,12 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
/* Double the boost at each request */
if (sg_cpu->iowait_boost) {
- sg_cpu->iowait_boost <<= 1;
- if (sg_cpu->iowait_boost > sg_cpu->iowait_boost_max)
- sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
+ sg_cpu->iowait_boost = min(sg_cpu->iowait_boost << 1, SCHED_CAPACITY_SCALE);
return;
}
/* First wakeup after IO: start with minimum boost */
- sg_cpu->iowait_boost = sg_cpu->sg_policy->policy->min;
+ sg_cpu->iowait_boost = sg_cpu->min;
}
/**
@@ -373,47 +370,31 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
* This mechanism is designed to boost high frequently IO waiting tasks, while
* being more conservative on tasks which does sporadic IO operations.
*/
-static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
- unsigned long *util, unsigned long *max)
+static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
+ unsigned long util, unsigned long max)
{
- unsigned int boost_util, boost_max;
-
/* No boost currently required */
if (!sg_cpu->iowait_boost)
- return;
+ return util;
/* Reset boost if the CPU appears to have been idle enough */
if (sugov_iowait_reset(sg_cpu, time, false))
- return;
+ return util;
- /*
- * An IO waiting task has just woken up:
- * allow to further double the boost value
- */
- if (sg_cpu->iowait_boost_pending) {
- sg_cpu->iowait_boost_pending = false;
- } else {
+ if (!sg_cpu->iowait_boost_pending) {
/*
- * Otherwise: reduce the boost value and disable it when we
- * reach the minimum.
+ * No boost pending; reduce the boost value.
*/
sg_cpu->iowait_boost >>= 1;
- if (sg_cpu->iowait_boost < sg_cpu->sg_policy->policy->min) {
+ if (sg_cpu->iowait_boost < sg_cpu->min) {
sg_cpu->iowait_boost = 0;
- return;
+ return util;
}
}
- /*
- * Apply the current boost value: a CPU is boosted only if its current
- * utilization is smaller then the current IO boost level.
- */
- boost_util = sg_cpu->iowait_boost;
- boost_max = sg_cpu->iowait_boost_max;
- if (*util * boost_max < *max * boost_util) {
- *util = boost_util;
- *max = boost_max;
- }
+ sg_cpu->iowait_boost_pending = false;
+
+ return min(max(util, sg_cpu->iowait_boost), max);
}
#ifdef CONFIG_NO_HZ_COMMON
@@ -460,7 +441,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
util = sugov_get_util(sg_cpu);
max = sg_cpu->max;
- sugov_iowait_apply(sg_cpu, time, &util, &max);
+ util = sugov_iowait_apply(sg_cpu, time, util, max);
next_f = get_next_freq(sg_policy, util, max);
/*
* Do not reduce the frequency if the CPU has not been idle
@@ -500,7 +481,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
j_util = sugov_get_util(j_sg_cpu);
j_max = j_sg_cpu->max;
- sugov_iowait_apply(j_sg_cpu, time, &j_util, &j_max);
+ j_util = sugov_iowait_apply(j_sg_cpu, time, j_util, j_max);
if (j_util * max > j_max * util) {
util = j_util;
@@ -837,7 +818,9 @@ static int sugov_start(struct cpufreq_policy *policy)
memset(sg_cpu, 0, sizeof(*sg_cpu));
sg_cpu->cpu = cpu;
sg_cpu->sg_policy = sg_policy;
- sg_cpu->iowait_boost_max = policy->cpuinfo.max_freq;
+ sg_cpu->min =
+ (SCHED_CAPACITY_SCALE * policy->cpuinfo.min_freq) /
+ policy->cpuinfo.max_freq;
}
for_each_cpu(cpu, policy->cpus) {
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