* [PATCH] cpufreq: Avoid unnecessary locking in show() and store()
@ 2016-02-11 1:25 Rafael J. Wysocki
2016-02-12 6:31 ` Viresh Kumar
0 siblings, 1 reply; 6+ messages in thread
From: Rafael J. Wysocki @ 2016-02-11 1:25 UTC (permalink / raw)
To: Linux PM list; +Cc: Linux Kernel Mailing List, Viresh Kumar
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
The show() and store() routines in the cpufreq core don't need to
acquire all of the locks to check if the struct freq_attr they want
to use really provides the callbacks they need as expected, so change
them to avoid doing that.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/cpufreq/cpufreq.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)
Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -862,13 +862,11 @@ static ssize_t show(struct kobject *kobj
struct freq_attr *fattr = to_attr(attr);
ssize_t ret;
- down_read(&policy->rwsem);
-
- if (fattr->show)
- ret = fattr->show(policy, buf);
- else
- ret = -EIO;
+ if (!fattr->show)
+ return -EIO;
+ down_read(&policy->rwsem);
+ ret = fattr->show(policy, buf);
up_read(&policy->rwsem);
return ret;
@@ -881,20 +879,17 @@ static ssize_t store(struct kobject *kob
struct freq_attr *fattr = to_attr(attr);
ssize_t ret = -EINVAL;
- get_online_cpus();
-
- if (!cpu_online(policy->cpu))
- goto unlock;
+ if (!fattr->store)
+ return -EIO;
- down_write(&policy->rwsem);
+ get_online_cpus();
- if (fattr->store)
+ if (cpu_online(policy->cpu)) {
+ down_write(&policy->rwsem);
ret = fattr->store(policy, buf, count);
- else
- ret = -EIO;
+ up_write(&policy->rwsem);
+ }
- up_write(&policy->rwsem);
-unlock:
put_online_cpus();
return ret;
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] cpufreq: Avoid unnecessary locking in show() and store()
2016-02-11 1:25 [PATCH] cpufreq: Avoid unnecessary locking in show() and store() Rafael J. Wysocki
@ 2016-02-12 6:31 ` Viresh Kumar
2016-02-12 13:18 ` Rafael J. Wysocki
0 siblings, 1 reply; 6+ messages in thread
From: Viresh Kumar @ 2016-02-12 6:31 UTC (permalink / raw)
To: Rafael J. Wysocki; +Cc: Linux PM list, Linux Kernel Mailing List
On 11-02-16, 02:25, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> The show() and store() routines in the cpufreq core don't need to
> acquire all of the locks to check if the struct freq_attr they want
> to use really provides the callbacks they need as expected, so change
> them to avoid doing that.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/cpufreq/cpufreq.c | 27 +++++++++++----------------
> 1 file changed, 11 insertions(+), 16 deletions(-)
>
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -862,13 +862,11 @@ static ssize_t show(struct kobject *kobj
> struct freq_attr *fattr = to_attr(attr);
> ssize_t ret;
>
> - down_read(&policy->rwsem);
> -
> - if (fattr->show)
> - ret = fattr->show(policy, buf);
> - else
> - ret = -EIO;
> + if (!fattr->show)
> + return -EIO;
>
> + down_read(&policy->rwsem);
> + ret = fattr->show(policy, buf);
> up_read(&policy->rwsem);
>
> return ret;
> @@ -881,20 +879,17 @@ static ssize_t store(struct kobject *kob
> struct freq_attr *fattr = to_attr(attr);
> ssize_t ret = -EINVAL;
>
> - get_online_cpus();
> -
> - if (!cpu_online(policy->cpu))
> - goto unlock;
> + if (!fattr->store)
> + return -EIO;
>
> - down_write(&policy->rwsem);
> + get_online_cpus();
>
> - if (fattr->store)
> + if (cpu_online(policy->cpu)) {
> + down_write(&policy->rwsem);
> ret = fattr->store(policy, buf, count);
> - else
> - ret = -EIO;
> + up_write(&policy->rwsem);
> + }
>
> - up_write(&policy->rwsem);
> -unlock:
I have no problems with the patch as is, but how are we going to benefit from it
?
'if (fattr->show/store)' is never ever going to fail, unless we have a bug here.
So, even we may want to add a WARN_ON() for that case instead.
--
viresh
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] cpufreq: Avoid unnecessary locking in show() and store()
2016-02-12 6:31 ` Viresh Kumar
@ 2016-02-12 13:18 ` Rafael J. Wysocki
2016-02-12 15:58 ` Viresh Kumar
0 siblings, 1 reply; 6+ messages in thread
From: Rafael J. Wysocki @ 2016-02-12 13:18 UTC (permalink / raw)
To: Viresh Kumar; +Cc: Linux PM list, Linux Kernel Mailing List
On Friday, February 12, 2016 12:01:15 PM Viresh Kumar wrote:
> On 11-02-16, 02:25, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > The show() and store() routines in the cpufreq core don't need to
> > acquire all of the locks to check if the struct freq_attr they want
> > to use really provides the callbacks they need as expected, so change
> > them to avoid doing that.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> > drivers/cpufreq/cpufreq.c | 27 +++++++++++----------------
> > 1 file changed, 11 insertions(+), 16 deletions(-)
> >
> > Index: linux-pm/drivers/cpufreq/cpufreq.c
> > ===================================================================
> > --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> > +++ linux-pm/drivers/cpufreq/cpufreq.c
> > @@ -862,13 +862,11 @@ static ssize_t show(struct kobject *kobj
> > struct freq_attr *fattr = to_attr(attr);
> > ssize_t ret;
> >
> > - down_read(&policy->rwsem);
> > -
> > - if (fattr->show)
> > - ret = fattr->show(policy, buf);
> > - else
> > - ret = -EIO;
> > + if (!fattr->show)
> > + return -EIO;
> >
> > + down_read(&policy->rwsem);
> > + ret = fattr->show(policy, buf);
> > up_read(&policy->rwsem);
> >
> > return ret;
> > @@ -881,20 +879,17 @@ static ssize_t store(struct kobject *kob
> > struct freq_attr *fattr = to_attr(attr);
> > ssize_t ret = -EINVAL;
> >
> > - get_online_cpus();
> > -
> > - if (!cpu_online(policy->cpu))
> > - goto unlock;
> > + if (!fattr->store)
> > + return -EIO;
> >
> > - down_write(&policy->rwsem);
> > + get_online_cpus();
> >
> > - if (fattr->store)
> > + if (cpu_online(policy->cpu)) {
> > + down_write(&policy->rwsem);
> > ret = fattr->store(policy, buf, count);
> > - else
> > - ret = -EIO;
> > + up_write(&policy->rwsem);
> > + }
> >
> > - up_write(&policy->rwsem);
> > -unlock:
>
> I have no problems with the patch as is, but how are we going to benefit from it
> ?
>
> 'if (fattr->show/store)' is never ever going to fail, unless we have a bug here.
Well, having a check that never fails is certainly unuseful.
> So, even we may want to add a WARN_ON() for that case instead.
I can add WARN_ON()s just fine.
---
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH] cpufreq: Avoid unnecessary locking in show() and store()
The show() and store() routines in the cpufreq core don't need to
acquire all of the locks to check if the struct freq_attr they want
to use really provides the callbacks they need as expected, so change
them to avoid doing that.
While at it, add WARN_ON()s around those checks as they are only supposed
to ever fail if there's a bug in the code.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/cpufreq/cpufreq.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)
Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -862,13 +862,11 @@ static ssize_t show(struct kobject *kobj
struct freq_attr *fattr = to_attr(attr);
ssize_t ret;
- down_read(&policy->rwsem);
-
- if (fattr->show)
- ret = fattr->show(policy, buf);
- else
- ret = -EIO;
+ if (WARN_ON(!fattr->show))
+ return -EIO;
+ down_read(&policy->rwsem);
+ ret = fattr->show(policy, buf);
up_read(&policy->rwsem);
return ret;
@@ -881,20 +879,17 @@ static ssize_t store(struct kobject *kob
struct freq_attr *fattr = to_attr(attr);
ssize_t ret = -EINVAL;
- get_online_cpus();
-
- if (!cpu_online(policy->cpu))
- goto unlock;
+ if (WARN_ON(!fattr->store))
+ return -EIO;
- down_write(&policy->rwsem);
+ get_online_cpus();
- if (fattr->store)
+ if (cpu_online(policy->cpu)) {
+ down_write(&policy->rwsem);
ret = fattr->store(policy, buf, count);
- else
- ret = -EIO;
+ up_write(&policy->rwsem);
+ }
- up_write(&policy->rwsem);
-unlock:
put_online_cpus();
return ret;
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] cpufreq: Avoid unnecessary locking in show() and store()
2016-02-12 13:18 ` Rafael J. Wysocki
@ 2016-02-12 15:58 ` Viresh Kumar
2016-02-12 16:10 ` Rafael J. Wysocki
0 siblings, 1 reply; 6+ messages in thread
From: Viresh Kumar @ 2016-02-12 15:58 UTC (permalink / raw)
To: Rafael J. Wysocki; +Cc: Linux PM list, Linux Kernel Mailing List
On 12-02-16, 14:18, Rafael J. Wysocki wrote:
> Well, having a check that never fails is certainly unuseful.
>
> > So, even we may want to add a WARN_ON() for that case instead.
>
> I can add WARN_ON()s just fine.
What about dropping the check completely ?
--
viresh
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] cpufreq: Avoid unnecessary locking in show() and store()
2016-02-12 15:58 ` Viresh Kumar
@ 2016-02-12 16:10 ` Rafael J. Wysocki
2016-02-12 16:20 ` Viresh Kumar
0 siblings, 1 reply; 6+ messages in thread
From: Rafael J. Wysocki @ 2016-02-12 16:10 UTC (permalink / raw)
To: Viresh Kumar; +Cc: Linux PM list, Linux Kernel Mailing List
On Friday, February 12, 2016 09:28:29 PM Viresh Kumar wrote:
> On 12-02-16, 14:18, Rafael J. Wysocki wrote:
> > Well, having a check that never fails is certainly unuseful.
> >
> > > So, even we may want to add a WARN_ON() for that case instead.
> >
> > I can add WARN_ON()s just fine.
>
> What about dropping the check completely ?
Fine by me.
---
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH] cpufreq: Drop unnecessary checks from show() and store()
The show() and store() routines in the cpufreq core don't need to
check if the struct freq_attr they want to use really provides the
callbacks they need as expected (if that's not the case, it means
a bug in the code anyway), so change them to avoid doing that.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/cpufreq/cpufreq.c | 21 +++++----------------
1 file changed, 5 insertions(+), 16 deletions(-)
Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -863,12 +863,7 @@ static ssize_t show(struct kobject *kobj
ssize_t ret;
down_read(&policy->rwsem);
-
- if (fattr->show)
- ret = fattr->show(policy, buf);
- else
- ret = -EIO;
-
+ ret = fattr->show(policy, buf);
up_read(&policy->rwsem);
return ret;
@@ -883,18 +878,12 @@ static ssize_t store(struct kobject *kob
get_online_cpus();
- if (!cpu_online(policy->cpu))
- goto unlock;
-
- down_write(&policy->rwsem);
-
- if (fattr->store)
+ if (cpu_online(policy->cpu)) {
+ down_write(&policy->rwsem);
ret = fattr->store(policy, buf, count);
- else
- ret = -EIO;
+ up_write(&policy->rwsem);
+ }
- up_write(&policy->rwsem);
-unlock:
put_online_cpus();
return ret;
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] cpufreq: Avoid unnecessary locking in show() and store()
2016-02-12 16:10 ` Rafael J. Wysocki
@ 2016-02-12 16:20 ` Viresh Kumar
0 siblings, 0 replies; 6+ messages in thread
From: Viresh Kumar @ 2016-02-12 16:20 UTC (permalink / raw)
To: Rafael J. Wysocki; +Cc: Linux PM list, Linux Kernel Mailing List
On 12-02-16, 17:10, Rafael J. Wysocki wrote:
> On Friday, February 12, 2016 09:28:29 PM Viresh Kumar wrote:
> > On 12-02-16, 14:18, Rafael J. Wysocki wrote:
> > > Well, having a check that never fails is certainly unuseful.
> > >
> > > > So, even we may want to add a WARN_ON() for that case instead.
> > >
> > > I can add WARN_ON()s just fine.
> >
> > What about dropping the check completely ?
>
> Fine by me.
>
> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Subject: [PATCH] cpufreq: Drop unnecessary checks from show() and store()
>
> The show() and store() routines in the cpufreq core don't need to
> check if the struct freq_attr they want to use really provides the
> callbacks they need as expected (if that's not the case, it means
> a bug in the code anyway), so change them to avoid doing that.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/cpufreq/cpufreq.c | 21 +++++----------------
> 1 file changed, 5 insertions(+), 16 deletions(-)
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
--
viresh
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2016-02-12 16:20 UTC | newest]
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2016-02-11 1:25 [PATCH] cpufreq: Avoid unnecessary locking in show() and store() Rafael J. Wysocki
2016-02-12 6:31 ` Viresh Kumar
2016-02-12 13:18 ` Rafael J. Wysocki
2016-02-12 15:58 ` Viresh Kumar
2016-02-12 16:10 ` Rafael J. Wysocki
2016-02-12 16:20 ` Viresh Kumar
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