diff mbox

[v8,3/6] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path

Message ID 1458273857.6622.75.camel@neuling.org (mailing list archive)
State Superseded, archived
Headers show

Commit Message

Michael Neuling March 18, 2016, 4:04 a.m. UTC 
On Wed, 2016-02-03 at 01:11 +0530, Shilpasri G Bhat wrote:

> cpu_to_chip_id() does a DT walk through to find out the chip id by
> taking a contended device tree lock. This adds an unnecessary overhead
> in a hot path. So instead of calling cpu_to_chip_id() everytime cache
> the chip ids for all cores in the array 'core_to_chip_map' and use it
> in the hotpath.
> 
> Reported-by: Anton Blanchard <anton@samba.org>
> Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> No changes from v7.

How about this instead?  It removes the linear lookup and seems a lot
less complex.

Mikey

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Comments

Benjamin Herrenschmidt March 18, 2016, 10:37 p.m. UTC | #1 
On Fri, 2016-03-18 at 15:04 +1100, Michael Neuling wrote:
> 
>  static int nr_chips;
> +static DEFINE_PER_CPU(unsigned int, chip_id);
>  
>  /*
>   * Note: The set of pstates consists of contiguous integers, the
> @@ -317,9 +318,7 @@ static void powernv_cpufreq_throttle_check(void
> *data)
>  
>         pmsr = get_pmspr(SPRN_PMSR);
>  
> -       for (i = 0; i < nr_chips; i++)
> -               if (chips[i].id == cpu_to_chip_id(cpu))
> -                       break;
> +       i = this_cpu_read(chip_id);

Except it's not a chip_id, so your patch confused me for a good 2mn ...
Call it chip_idx maybe ? ie, index.

Cheers,
Ben.

>         /* Check for Pmax Capping */
>         pmsr_pmax = (s8)PMSR_MAX(pmsr);
> @@ -560,6 +559,7 @@ static int init_chip_info(void)
>         for_each_possible_cpu(cpu) {
>                 unsigned int id = cpu_to_chip_id(cpu);
>  
> +               per_cpu(chip_id, cpu) = nr_chips;
>                 if (prev_chip_id != id) {
>                         prev_chip_id = id;
>                         chip[nr_chips++] = id;
> _______________________________________________

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Michael Neuling March 18, 2016, 11:20 p.m. UTC | #2 
On Sat, 2016-03-19 at 09:37 +1100, Benjamin Herrenschmidt wrote:
> On Fri, 2016-03-18 at 15:04 +1100, Michael Neuling wrote:
> > 
> >  static int nr_chips;
> > +static DEFINE_PER_CPU(unsigned int, chip_id);
> >  
> >  /*
> >   * Note: The set of pstates consists of contiguous integers, the
> > @@ -317,9 +318,7 @@ static void powernv_cpufreq_throttle_check(void
> > *data)
> >  
> >         pmsr = get_pmspr(SPRN_PMSR);
> >  
> > -       for (i = 0; i < nr_chips; i++)
> > -               if (chips[i].id == cpu_to_chip_id(cpu))
> > -                       break;
> > +       i = this_cpu_read(chip_id);
> 
> Except it's not a chip_id, so your patch confused me for a good 2mn
> ...
> Call it chip_idx maybe ? ie, index.

Yeah, it was a badly named variable but I changed it even more and
Shilpasri rebased it here:

http://patchwork.ozlabs.org/patch/599523/

Mikey
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diff mbox

Patch

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index 547890f..d63d2cb 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -52,6 +52,7 @@  static struct chip {
 } *chips;
 
 static int nr_chips;
+static DEFINE_PER_CPU(unsigned int, chip_id);
 
 /*
  * Note: The set of pstates consists of contiguous integers, the
@@ -317,9 +318,7 @@  static void powernv_cpufreq_throttle_check(void *data)
 
 	pmsr = get_pmspr(SPRN_PMSR);
 
-	for (i = 0; i < nr_chips; i++)
-		if (chips[i].id == cpu_to_chip_id(cpu))
-			break;
+	i = this_cpu_read(chip_id);
 
 	/* Check for Pmax Capping */
 	pmsr_pmax = (s8)PMSR_MAX(pmsr);
@@ -560,6 +559,7 @@  static int init_chip_info(void)
 	for_each_possible_cpu(cpu) {
 		unsigned int id = cpu_to_chip_id(cpu);
 
+		per_cpu(chip_id, cpu) = nr_chips;
 		if (prev_chip_id != id) {
 			prev_chip_id = id;
 			chip[nr_chips++] = id;