* [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update
@ 2023-07-03 14:52 Uros Bizjak
2023-07-05 14:53 ` Dave Jiang
2023-08-01 18:45 ` Vinod Koul
0 siblings, 2 replies; 4+ messages in thread
From: Uros Bizjak @ 2023-07-03 14:52 UTC (permalink / raw)
To: dmaengine, linux-kernel; +Cc: Uros Bizjak, Fenghua Yu, Dave Jiang, Vinod Koul
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(-)
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);
--
2.41.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update
2023-07-03 14:52 [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update Uros Bizjak
@ 2023-07-05 14:53 ` Dave Jiang
2023-07-10 21:28 ` Tom Zanussi
2023-08-01 18:45 ` Vinod Koul
1 sibling, 1 reply; 4+ messages in thread
From: Dave Jiang @ 2023-07-05 14:53 UTC (permalink / raw)
To: Uros Bizjak, dmaengine, linux-kernel; +Cc: Fenghua Yu, Vinod Koul, Zanussi, Tom
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);
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update
2023-07-05 14:53 ` Dave Jiang
@ 2023-07-10 21:28 ` Tom Zanussi
0 siblings, 0 replies; 4+ messages in thread
From: Tom Zanussi @ 2023-07-10 21:28 UTC (permalink / raw)
To: Dave Jiang, Uros Bizjak, dmaengine, linux-kernel
Cc: Fenghua Yu, Vinod Koul, Zanussi, Tom
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);
> >
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update
2023-07-03 14:52 [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update Uros Bizjak
2023-07-05 14:53 ` Dave Jiang
@ 2023-08-01 18:45 ` Vinod Koul
1 sibling, 0 replies; 4+ messages in thread
From: Vinod Koul @ 2023-08-01 18:45 UTC (permalink / raw)
To: dmaengine, linux-kernel, Uros Bizjak; +Cc: Fenghua Yu, Dave Jiang
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,
--
~Vinod
^ permalink raw reply [flat|nested] 4+ messages in thread
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2023-07-03 14:52 [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update Uros Bizjak
2023-07-05 14:53 ` Dave Jiang
2023-07-10 21:28 ` Tom Zanussi
2023-08-01 18:45 ` Vinod Koul
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