[PATCH-next v2 0/2] cpufreq: powernv: Fixes for Global pstate management

[PATCH-next v2 0/2] cpufreq: powernv: Fixes for Global pstate management

[Akshay Adiga]

Fixes are based on patch https://patchwork.ozlabs.org/patch/612058/ which
is in Rafael's linux-next.

- Patch [1] fixes WARN_ON in powernv_target_index()
- Patch [2] Deleting any pending timer to saves an unnecessary irq call
 in powernv_target_index()

Akshay Adiga (2):
  cpufreq: powernv: Move smp_call_function_any() out of irq safe block
  cpufreq: powernv: del_timer_sync when global and local pstate are
    equal

 drivers/cpufreq/powernv-cpufreq.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

-- 
2.5.5

[PATCH-next v2 1/2] cpufreq: powernv: Move smp_call_function_any() out of irq safe block

[Akshay Adiga]

Fix a WARN_ON caused by smp_call_function_any() when irq is disabled,
because of changes made in the patch ('cpufreq: powernv: Ramp-down
 global pstate slower than local-pstate')
https://patchwork.ozlabs.org/patch/612058/

 WARNING: CPU: 0 PID: 4 at kernel/smp.c:291
smp_call_function_single+0x170/0x180

 Call Trace:
 [c0000007f648f9f0] [c0000007f648fa90] 0xc0000007f648fa90 (unreliable)
 [c0000007f648fa30] [c0000000001430e0] smp_call_function_any+0x170/0x1c0
 [c0000007f648fa90] [c0000000007b4b00]
powernv_cpufreq_target_index+0xe0/0x250
 [c0000007f648fb00] [c0000000007ac9dc]
__cpufreq_driver_target+0x20c/0x3d0
 [c0000007f648fbc0] [c0000000007b1b4c] od_dbs_timer+0xcc/0x260
 [c0000007f648fc10] [c0000000007b3024] dbs_work_handler+0x54/0xa0
 [c0000007f648fc50] [c0000000000c49a8] process_one_work+0x1d8/0x590
 [c0000007f648fce0] [c0000000000c4e08] worker_thread+0xa8/0x660
 [c0000007f648fd80] [c0000000000cca88] kthread+0x108/0x130
 [c0000007f648fe30] [c0000000000095e8] ret_from_kernel_thread+0x5c/0x74

- Calling smp_call_function_any() with interrupt disabled (through
 spin_lock_irqsave) could cause a deadlock, as smp_call_function_any()
 relies on the IPI to complete. This is detected in the
 smp_call_function_any() call and hence the WARN_ON.

- As the spinlock (gpstates->lock) is only used to synchronize access of
 global_pstate_info  between timer irq handler and target_index calls. And
 the timer irq handler just try_locks() hence it would not cause a
 deadlock. Hence could do without making spinlocks irq safe.

- As the smp_call_function_any() is a blocking call and does not access
 global_pstates_info, it could reduce the critcal section by moving
 smp_call_function_any() after giving up the lock.

Reported-by: Abdul Haleem <abdhalee@linux.vnet.linux.com>
Signed-off-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
---
Patch is based on Rafael's linux-next
 drivers/cpufreq/powernv-cpufreq.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index 144c732..1f0e20c 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -581,9 +581,10 @@ void gpstate_timer_handler(unsigned long data)
 	gpstates->last_gpstate = freq_data.gpstate_id;
 	gpstates->last_lpstate = freq_data.pstate_id;
 
+	spin_unlock(&gpstates->gpstate_lock);
+
 	/* Timer may get migrated to a different cpu on cpu hot unplug */
 	smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1);
-	spin_unlock(&gpstates->gpstate_lock);
 }
 
 /*
@@ -596,7 +597,6 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
 {
 	struct powernv_smp_call_data freq_data;
 	unsigned int cur_msec, gpstate_id;
-	unsigned long flags;
 	struct global_pstate_info *gpstates = policy->driver_data;
 
 	if (unlikely(rebooting) && new_index != get_nominal_index())
@@ -607,7 +607,7 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
 
 	cur_msec = jiffies_to_msecs(get_jiffies_64());
 
-	spin_lock_irqsave(&gpstates->gpstate_lock, flags);
+	spin_lock(&gpstates->gpstate_lock);
 	freq_data.pstate_id = powernv_freqs[new_index].driver_data;
 
 	if (!gpstates->last_sampled_time) {
@@ -654,13 +654,14 @@ gpstates_done:
 	gpstates->last_gpstate = freq_data.gpstate_id;
 	gpstates->last_lpstate = freq_data.pstate_id;
 
+	spin_unlock(&gpstates->gpstate_lock);
+
 	/*
 	 * Use smp_call_function to send IPI and execute the
 	 * mtspr on target CPU.  We could do that without IPI
 	 * if current CPU is within policy->cpus (core)
 	 */
 	smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1);
-	spin_unlock_irqrestore(&gpstates->gpstate_lock, flags);
 	return 0;
 }
 
-- 
2.5.5

[PATCH-next v2 2/2] cpufreq: powernv: del_timer_sync when global and local pstate are equal

[Akshay Adiga]

When global and local pstate are equal in a powernv_target_index() call,
we don't queue a timer. But we may have timer already queued for future.
This could cause the timer to fire one additional time for no use.

Signed-off-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
---
Patch is based on Rafael's linux-next
 drivers/cpufreq/powernv-cpufreq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index 1f0e20c..54c4536 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -647,6 +647,8 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
 	 */
 	if (gpstate_id != freq_data.pstate_id)
 		queue_gpstate_timer(gpstates);
+	else
+		del_timer_sync(&gpstates->timer);
 
 gpstates_done:
 	freq_data.gpstate_id = gpstate_id;
-- 
2.5.5

Re: [PATCH-next v2 0/2] cpufreq: powernv: Fixes for Global pstate management

[Akshay Adiga]

On 05/03/2016 08:49 PM, Akshay Adiga wrote:

> Fixes are based on patch https://patchwork.ozlabs.org/patch/612058/ which
> is in Rafael's linux-next.
>
> - Patch [1] fixes WARN_ON in powernv_target_index()
> - Patch [2] Deleting any pending timer to saves an unnecessary irq call
>   in powernv_target_index()
>
> Akshay Adiga (2):
>    cpufreq: powernv: Move smp_call_function_any() out of irq safe block
>    cpufreq: powernv: del_timer_sync when global and local pstate are
>      equal
>
>   drivers/cpufreq/powernv-cpufreq.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
>
Does this look good ? Anything i should do ?


Regards
Akshay Adiga

Re: [PATCH-next v2 0/2] cpufreq: powernv: Fixes for Global pstate management

[Viresh Kumar]

On 03-05-16, 20:49, Akshay Adiga wrote:
> Fixes are based on patch https://patchwork.ozlabs.org/patch/612058/ which
> is in Rafael's linux-next.
> 
> - Patch [1] fixes WARN_ON in powernv_target_index()
> - Patch [2] Deleting any pending timer to saves an unnecessary irq call
>  in powernv_target_index()
> 
> Akshay Adiga (2):
>   cpufreq: powernv: Move smp_call_function_any() out of irq safe block
>   cpufreq: powernv: del_timer_sync when global and local pstate are
>     equal

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh

Re: [PATCH-next v2 0/2] cpufreq: powernv: Fixes for Global pstate management

[Rafael J. Wysocki]

On Monday, May 09, 2016 09:02:04 PM Viresh Kumar wrote:
> On 03-05-16, 20:49, Akshay Adiga wrote:
> > Fixes are based on patch https://patchwork.ozlabs.org/patch/612058/ which
> > is in Rafael's linux-next.
> > 
> > - Patch [1] fixes WARN_ON in powernv_target_index()
> > - Patch [2] Deleting any pending timer to saves an unnecessary irq call
> >  in powernv_target_index()
> > 
> > Akshay Adiga (2):
> >   cpufreq: powernv: Move smp_call_function_any() out of irq safe block
> >   cpufreq: powernv: del_timer_sync when global and local pstate are
> >     equal
> 
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

Both [1-2/2] applied, thanks!