diff mbox series

dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update

Message ID 20230703145346.5206-1-ubizjak@gmail.com
State New
Headers
Series dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update |

Commit Message

Uros Bizjak July 3, 2023, 2:52 p.m. UTC 
  Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old
in perfmon_pmu_event_update.  x86 CMPXCHG instruction returns success in
ZF flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.

No functional change intended.

Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
 drivers/dma/idxd/perfmon.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Comments

Dave Jiang July 5, 2023, 2:53 p.m. UTC | #1 
On 7/3/23 07:52, Uros Bizjak wrote:
> Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old
> in perfmon_pmu_event_update.  x86 CMPXCHG instruction returns success in
> ZF flag, so this change saves a compare after cmpxchg (and related move
> instruction in front of cmpxchg).
> 
> Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
> fails. There is no need to re-read the value in the loop.
> 
> No functional change intended.
> 
> Cc: Fenghua Yu <fenghua.yu@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Vinod Koul <vkoul@kernel.org>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>


Cc: Tom Zanussi

Tom do you mind review this patch? Thanks!

> ---
>   drivers/dma/idxd/perfmon.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dma/idxd/perfmon.c b/drivers/dma/idxd/perfmon.c
> index d73004f47cf4..fdda6d604262 100644
> --- a/drivers/dma/idxd/perfmon.c
> +++ b/drivers/dma/idxd/perfmon.c
> @@ -245,12 +245,11 @@ static void perfmon_pmu_event_update(struct perf_event *event)
>   	int shift = 64 - idxd->idxd_pmu->counter_width;
>   	struct hw_perf_event *hwc = &event->hw;
>   
> +	prev_raw_count = local64_read(&hwc->prev_count);
>   	do {
> -		prev_raw_count = local64_read(&hwc->prev_count);
>   		new_raw_count = perfmon_pmu_read_counter(event);
> -	} while (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
> -			new_raw_count) != prev_raw_count);
> -
> +	} while (!local64_try_cmpxchg(&hwc->prev_count,
> +				      &prev_raw_count, new_raw_count));
>   	n = (new_raw_count << shift);
>   	p = (prev_raw_count << shift);
>
Tom Zanussi July 10, 2023, 9:28 p.m. UTC | #2 
On Wed, 2023-07-05 at 07:53 -0700, Dave Jiang wrote:
> 
> 
> On 7/3/23 07:52, Uros Bizjak wrote:
> > Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old
> > in perfmon_pmu_event_update.  x86 CMPXCHG instruction returns success in
> > ZF flag, so this change saves a compare after cmpxchg (and related move
> > instruction in front of cmpxchg).
> > 
> > Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
> > fails. There is no need to re-read the value in the loop.
> > 
> > No functional change intended.
> > 
> > Cc: Fenghua Yu <fenghua.yu@intel.com>
> > Cc: Dave Jiang <dave.jiang@intel.com>
> > Cc: Vinod Koul <vkoul@kernel.org>
> > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> 
> 
> Cc: Tom Zanussi
> 
> Tom do you mind review this patch? Thanks!

Looks fine to me.

Thanks,

Reviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>

> 
> > ---
> >   drivers/dma/idxd/perfmon.c | 7 +++----
> >   1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/dma/idxd/perfmon.c b/drivers/dma/idxd/perfmon.c
> > index d73004f47cf4..fdda6d604262 100644
> > --- a/drivers/dma/idxd/perfmon.c
> > +++ b/drivers/dma/idxd/perfmon.c
> > @@ -245,12 +245,11 @@ static void perfmon_pmu_event_update(struct perf_event *event)
> >         int shift = 64 - idxd->idxd_pmu->counter_width;
> >         struct hw_perf_event *hwc = &event->hw;
> >   
> > +       prev_raw_count = local64_read(&hwc->prev_count);
> >         do {
> > -               prev_raw_count = local64_read(&hwc->prev_count);
> >                 new_raw_count = perfmon_pmu_read_counter(event);
> > -       } while (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
> > -                       new_raw_count) != prev_raw_count);
> > -
> > +       } while (!local64_try_cmpxchg(&hwc->prev_count,
> > +                                     &prev_raw_count, new_raw_count));
> >         n = (new_raw_count << shift);
> >         p = (prev_raw_count << shift);
> >
Vinod Koul Aug. 1, 2023, 6:45 p.m. UTC | #3 
On Mon, 03 Jul 2023 16:52:37 +0200, Uros Bizjak wrote:
> Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old
> in perfmon_pmu_event_update.  x86 CMPXCHG instruction returns success in
> ZF flag, so this change saves a compare after cmpxchg (and related move
> instruction in front of cmpxchg).
> 
> Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
> fails. There is no need to re-read the value in the loop.
> 
> [...]

Applied, thanks!

[1/1] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update
      commit: cae701b9ccf128edea26982f73178087fc3ad180

Best regards,
diff mbox series

Patch

diff --git a/drivers/dma/idxd/perfmon.c b/drivers/dma/idxd/perfmon.c
index d73004f47cf4..fdda6d604262 100644
--- a/drivers/dma/idxd/perfmon.c
+++ b/drivers/dma/idxd/perfmon.c
@@ -245,12 +245,11 @@  static void perfmon_pmu_event_update(struct perf_event *event)
 	int shift = 64 - idxd->idxd_pmu->counter_width;
 	struct hw_perf_event *hwc = &event->hw;
 
+	prev_raw_count = local64_read(&hwc->prev_count);
 	do {
-		prev_raw_count = local64_read(&hwc->prev_count);
 		new_raw_count = perfmon_pmu_read_counter(event);
-	} while (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
-			new_raw_count) != prev_raw_count);
-
+	} while (!local64_try_cmpxchg(&hwc->prev_count,
+				      &prev_raw_count, new_raw_count));
 	n = (new_raw_count << shift);
 	p = (prev_raw_count << shift);