From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Viresh Kumar <viresh.kumar@linaro.org>, linux-pm@vger.kernel.org
Cc: linaro-kernel@lists.linaro.org, ashwin.chaugule@linaro.org,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH][experimantal] cpufreq: governor: Use an atomic variable for synchronization
Date: Tue, 08 Dec 2015 01:39:53 +0100 [thread overview]
Message-ID: <4910771.IIQSzHPqps@vostro.rjw.lan> (raw)
In-Reply-To: <2389125.q3qMOpRs8O@vostro.rjw.lan>
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Use the observation that if skip_work in struct cpu_common_dbs_info
is an atomic_t variable, the code may be rearranged to avoid using
the timer_lock spinlock in which case that lock is not necessary any
more.
Make that change and drop timer_lock.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
This is on top of my current linux-next branch. Completely experimental and
untested.
---
drivers/cpufreq/cpufreq_governor.c | 29 +++++++----------------------
drivers/cpufreq/cpufreq_governor.h | 9 ++-------
2 files changed, 9 insertions(+), 29 deletions(-)
Index: linux-pm/drivers/cpufreq/cpufreq_governor.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq_governor.c
+++ linux-pm/drivers/cpufreq/cpufreq_governor.c
@@ -186,22 +186,15 @@ static inline void gov_cancel_timers(str
void gov_cancel_work(struct cpu_common_dbs_info *shared)
{
- unsigned long flags;
-
/*
* No work will be queued from timer handlers after skip_work is
* updated. And so we can safely cancel the work first and then the
* timers.
*/
- spin_lock_irqsave(&shared->timer_lock, flags);
- shared->skip_work++;
- spin_unlock_irqrestore(&shared->timer_lock, flags);
-
+ atomic_inc(&shared->skip_work);
cancel_work_sync(&shared->work);
-
gov_cancel_timers(shared->policy);
-
- shared->skip_work = 0;
+ atomic_set(&shared->skip_work, 0);
}
/* Will return if we need to evaluate cpu load again or not */
@@ -229,7 +222,6 @@ static void dbs_work_handler(struct work
struct cpufreq_policy *policy;
struct dbs_data *dbs_data;
unsigned int sampling_rate, delay;
- unsigned long flags;
bool eval_load;
policy = shared->policy;
@@ -258,9 +250,7 @@ static void dbs_work_handler(struct work
delay = dbs_data->cdata->gov_dbs_timer(policy, eval_load);
mutex_unlock(&shared->timer_mutex);
- spin_lock_irqsave(&shared->timer_lock, flags);
- shared->skip_work--;
- spin_unlock_irqrestore(&shared->timer_lock, flags);
+ atomic_dec(&shared->skip_work);
gov_add_timers(policy, delay);
}
@@ -269,9 +259,6 @@ static void dbs_timer_handler(unsigned l
{
struct cpu_dbs_info *cdbs = (struct cpu_dbs_info *)data;
struct cpu_common_dbs_info *shared = cdbs->shared;
- unsigned long flags;
-
- spin_lock_irqsave(&shared->timer_lock, flags);
/*
* Timer handler isn't allowed to queue work at the moment, because:
@@ -279,12 +266,10 @@ static void dbs_timer_handler(unsigned l
* - We are stopping the governor
* - Or we are updating the sampling rate of ondemand governor
*/
- if (!shared->skip_work) {
- shared->skip_work++;
+ if (atomic_inc_return(&shared->skip_work) > 1)
+ atomic_dec(&shared->skip_work);
+ else
queue_work(system_wq, &shared->work);
- }
-
- spin_unlock_irqrestore(&shared->timer_lock, flags);
}
static void set_sampling_rate(struct dbs_data *dbs_data,
@@ -315,7 +300,7 @@ static int alloc_common_dbs_info(struct
cdata->get_cpu_cdbs(j)->shared = shared;
mutex_init(&shared->timer_mutex);
- spin_lock_init(&shared->timer_lock);
+ atomic_set(&shared->skip_work, 0);
INIT_WORK(&shared->work, dbs_work_handler);
return 0;
}
Index: linux-pm/drivers/cpufreq/cpufreq_governor.h
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq_governor.h
+++ linux-pm/drivers/cpufreq/cpufreq_governor.h
@@ -17,6 +17,7 @@
#ifndef _CPUFREQ_GOVERNOR_H
#define _CPUFREQ_GOVERNOR_H
+#include <linux/atomic.h>
#include <linux/cpufreq.h>
#include <linux/kernel_stat.h>
#include <linux/module.h>
@@ -137,14 +138,8 @@ struct cpu_common_dbs_info {
*/
struct mutex timer_mutex;
- /*
- * Per policy lock that serializes access to queuing work from timer
- * handlers.
- */
- spinlock_t timer_lock;
-
ktime_t time_stamp;
- unsigned int skip_work;
+ atomic_t skip_work;
struct work_struct work;
};
next prev parent reply other threads:[~2015-12-08 0:09 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1449115453.git.viresh.kumar@linaro.org>
2015-12-03 4:07 ` [PATCH V2 1/6] cpufreq: ondemand: Update sampling rate only for concerned policies Viresh Kumar
2015-12-03 4:07 ` [PATCH V2 2/6] cpufreq: ondemand: Work is guaranteed to be pending Viresh Kumar
2015-12-03 4:07 ` [PATCH V2 3/6] cpufreq: governor: Pass policy as argument to ->gov_dbs_timer() Viresh Kumar
2015-12-03 4:07 ` [PATCH V2 4/6] cpufreq: governor: initialize/destroy timer_mutex with 'shared' Viresh Kumar
2015-12-03 4:07 ` [PATCH V2 5/6] cpufreq: governor: replace per-cpu delayed work with timers Viresh Kumar
2015-12-04 1:18 ` Rafael J. Wysocki
2015-12-04 6:11 ` Viresh Kumar
2015-12-05 2:14 ` Rafael J. Wysocki
2015-12-05 4:10 ` Viresh Kumar
2015-12-07 1:28 ` Rafael J. Wysocki
2015-12-07 7:50 ` Viresh Kumar
2015-12-07 22:43 ` Rafael J. Wysocki
2015-12-07 23:17 ` Rafael J. Wysocki
2015-12-08 0:39 ` Rafael J. Wysocki [this message]
2015-12-08 6:59 ` [PATCH][experimantal] cpufreq: governor: Use an atomic variable for synchronization Viresh Kumar
2015-12-08 13:30 ` Rafael J. Wysocki
2015-12-08 13:36 ` Viresh Kumar
2015-12-08 14:19 ` Rafael J. Wysocki
2015-12-08 13:55 ` Viresh Kumar
2015-12-08 14:30 ` Rafael J. Wysocki
2015-12-08 14:56 ` Viresh Kumar
2015-12-08 16:42 ` Rafael J. Wysocki
2015-12-08 16:34 ` Viresh Kumar
2015-12-08 6:46 ` [PATCH V2 5/6] cpufreq: governor: replace per-cpu delayed work with timers Viresh Kumar
2015-12-08 6:56 ` Viresh Kumar
2015-12-08 13:18 ` Rafael J. Wysocki
2015-12-08 13:30 ` Viresh Kumar
2015-12-08 14:04 ` Rafael J. Wysocki
2015-12-04 6:13 ` [PATCH V3 " Viresh Kumar
2015-12-09 2:04 ` [PATCH V4 " Viresh Kumar
2015-12-09 22:06 ` Rafael J. Wysocki
2015-12-10 2:36 ` Viresh Kumar
2015-12-10 22:17 ` Rafael J. Wysocki
2015-12-11 1:42 ` Viresh Kumar
2015-12-03 4:07 ` [PATCH V2 6/6] cpufreq: ondemand: update update_sampling_rate() to make it more efficient Viresh Kumar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4910771.IIQSzHPqps@vostro.rjw.lan \
--to=rjw@rjwysocki.net \
--cc=ashwin.chaugule@linaro.org \
--cc=linaro-kernel@lists.linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=rafael.j.wysocki@intel.com \
--cc=viresh.kumar@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).