diff mbox

[1/3] cpuidle: powernv: Don't bounce between low and very low thread priority

Message ID 20170403215414.16951-1-anton@ozlabs.org (mailing list archive)
State Mainlined
Delegated to: Rafael Wysocki
Headers show

Commit Message

Anton Blanchard April 3, 2017, 9:54 p.m. UTC
From: Anton Blanchard <anton@samba.org>

The core of snooze_loop() continually bounces between low and very
low thread priority. Changing thread priorities is an expensive
operation that can negatively impact other threads on a core.

All CPUs that can run PowerNV support very low priority, so we can
avoid the change completely.

Signed-off-by: Anton Blanchard <anton@samba.org>
---
 drivers/cpuidle/cpuidle-powernv.c | 1 -
 1 file changed, 1 deletion(-)

Comments

Nicholas Piggin April 3, 2017, 11:52 p.m. UTC | #1
On Tue,  4 Apr 2017 07:54:12 +1000
Anton Blanchard <anton@ozlabs.org> wrote:

> From: Anton Blanchard <anton@samba.org>
> 
> The core of snooze_loop() continually bounces between low and very
> low thread priority. Changing thread priorities is an expensive
> operation that can negatively impact other threads on a core.
> 
> All CPUs that can run PowerNV support very low priority, so we can
> avoid the change completely.

This looks good. I have HMT_lowest() which does alt feature patching
we can use for pseries and default idle code.
Vaidyanathan Srinivasan April 4, 2017, 4:04 a.m. UTC | #2
* Anton Blanchard <anton@ozlabs.org> [2017-04-04 07:54:12]:

> From: Anton Blanchard <anton@samba.org>
> 
> The core of snooze_loop() continually bounces between low and very
> low thread priority. Changing thread priorities is an expensive
> operation that can negatively impact other threads on a core.
> 
> All CPUs that can run PowerNV support very low priority, so we can
> avoid the change completely.
> 
> Signed-off-by: Anton Blanchard <anton@samba.org>

Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>

> ---
>  drivers/cpuidle/cpuidle-powernv.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> index cda8f62d555b..9d9f164894eb 100644
> --- a/drivers/cpuidle/cpuidle-powernv.c
> +++ b/drivers/cpuidle/cpuidle-powernv.c
> @@ -57,7 +57,6 @@ static int snooze_loop(struct cpuidle_device *dev,
>  	snooze_exit_time = get_tb() + snooze_timeout;
>  	ppc64_runlatch_off();
>  	while (!need_resched()) {
> -		HMT_low();
>  		HMT_very_low();
>  		if (snooze_timeout_en && get_tb() > snooze_exit_time)
>  			break;


HMT_low() is legacy and can be removed for powernv platforms.

--Vaidy
Vaidyanathan Srinivasan April 4, 2017, 4:13 a.m. UTC | #3
* Nicholas Piggin <npiggin@gmail.com> [2017-04-04 09:52:07]:

> On Tue,  4 Apr 2017 07:54:12 +1000
> Anton Blanchard <anton@ozlabs.org> wrote:
> 
> > From: Anton Blanchard <anton@samba.org>
> > 
> > The core of snooze_loop() continually bounces between low and very
> > low thread priority. Changing thread priorities is an expensive
> > operation that can negatively impact other threads on a core.
> > 
> > All CPUs that can run PowerNV support very low priority, so we can
> > avoid the change completely.
> 
> This looks good. I have HMT_lowest() which does alt feature patching
> we can use for pseries and default idle code.

Alternatively, if we are going to set priority only once in various
other places, HMT_low(); HMT_very_low(); should not add to extra
cycles.  Let me code that up.

--Vaidy
diff mbox

Patch

diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index cda8f62d555b..9d9f164894eb 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c
@@ -57,7 +57,6 @@  static int snooze_loop(struct cpuidle_device *dev,
 	snooze_exit_time = get_tb() + snooze_timeout;
 	ppc64_runlatch_off();
 	while (!need_resched()) {
-		HMT_low();
 		HMT_very_low();
 		if (snooze_timeout_en && get_tb() > snooze_exit_time)
 			break;