From: Pavel Begunkov <[email protected]>
cmpxchg() with an immediate value could be replaced with less expensive
xchg(). The same true if new value don't _depend_ on the old one.
In the second block, atomic_cmpxchg() return value isn't checked, so
after atomic_cmpxchg() -> atomic_xchg() conversion it could be replaced
with atomic_set(). Comparison with atomic_read() in the second chunk was
left as an optimisation (if that was the initial intention).
Signed-off-by: Pavel Begunkov <[email protected]>
---
lib/sbitmap.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 155fe38756ec..7d7e0e278523 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -37,9 +37,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
/*
* First get a stable cleared mask, setting the old mask to 0.
*/
- do {
- mask = sb->map[index].cleared;
- } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask);
+ mask = xchg(&sb->map[index].cleared, 0);
/*
* Now clear the masked bits in our free word
@@ -527,10 +525,8 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
struct sbq_wait_state *ws = &sbq->ws[wake_index];
if (waitqueue_active(&ws->wait)) {
- int o = atomic_read(&sbq->wake_index);
-
- if (wake_index != o)
- atomic_cmpxchg(&sbq->wake_index, o, wake_index);
+ if (wake_index != atomic_read(&sbq->wake_index))
+ atomic_set(&sbq->wake_index, wake_index);
return ws;
}
--
2.21.0
Ping?
On 23/05/2019 08:39, Pavel Begunkov (Silence) wrote:
> From: Pavel Begunkov <[email protected]>
>
> cmpxchg() with an immediate value could be replaced with less expensive
> xchg(). The same true if new value don't _depend_ on the old one.
>
> In the second block, atomic_cmpxchg() return value isn't checked, so
> after atomic_cmpxchg() -> atomic_xchg() conversion it could be replaced
> with atomic_set(). Comparison with atomic_read() in the second chunk was
> left as an optimisation (if that was the initial intention).
>
> Signed-off-by: Pavel Begunkov <[email protected]>
> ---
> lib/sbitmap.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index 155fe38756ec..7d7e0e278523 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -37,9 +37,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
> /*
> * First get a stable cleared mask, setting the old mask to 0.
> */
> - do {
> - mask = sb->map[index].cleared;
> - } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask);
> + mask = xchg(&sb->map[index].cleared, 0);
>
> /*
> * Now clear the masked bits in our free word
> @@ -527,10 +525,8 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
> struct sbq_wait_state *ws = &sbq->ws[wake_index];
>
> if (waitqueue_active(&ws->wait)) {
> - int o = atomic_read(&sbq->wake_index);
> -
> - if (wake_index != o)
> - atomic_cmpxchg(&sbq->wake_index, o, wake_index);
> + if (wake_index != atomic_read(&sbq->wake_index))
> + atomic_set(&sbq->wake_index, wake_index);
> return ws;
> }
>
>
--
Yours sincerely,
Pavel Begunkov
Omar?
On 6/29/19 9:42 AM, Pavel Begunkov wrote:
> Ping?
>
> On 23/05/2019 08:39, Pavel Begunkov (Silence) wrote:
>> From: Pavel Begunkov <[email protected]>
>>
>> cmpxchg() with an immediate value could be replaced with less expensive
>> xchg(). The same true if new value don't _depend_ on the old one.
>>
>> In the second block, atomic_cmpxchg() return value isn't checked, so
>> after atomic_cmpxchg() -> atomic_xchg() conversion it could be replaced
>> with atomic_set(). Comparison with atomic_read() in the second chunk was
>> left as an optimisation (if that was the initial intention).
>>
>> Signed-off-by: Pavel Begunkov <[email protected]>
>> ---
>> lib/sbitmap.c | 10 +++-------
>> 1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
>> index 155fe38756ec..7d7e0e278523 100644
>> --- a/lib/sbitmap.c
>> +++ b/lib/sbitmap.c
>> @@ -37,9 +37,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
>> /*
>> * First get a stable cleared mask, setting the old mask to 0.
>> */
>> - do {
>> - mask = sb->map[index].cleared;
>> - } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask);
>> + mask = xchg(&sb->map[index].cleared, 0);
>>
>> /*
>> * Now clear the masked bits in our free word
>> @@ -527,10 +525,8 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
>> struct sbq_wait_state *ws = &sbq->ws[wake_index];
>>
>> if (waitqueue_active(&ws->wait)) {
>> - int o = atomic_read(&sbq->wake_index);
>> -
>> - if (wake_index != o)
>> - atomic_cmpxchg(&sbq->wake_index, o, wake_index);
>> + if (wake_index != atomic_read(&sbq->wake_index))
>> + atomic_set(&sbq->wake_index, wake_index);
>> return ws;
>> }
>>
>>
>
--
Jens Axboe
On Sat, Jun 29, 2019 at 08:42:23AM -0700, Pavel Begunkov wrote:
> Ping?
>
> On 23/05/2019 08:39, Pavel Begunkov (Silence) wrote:
> > From: Pavel Begunkov <[email protected]>
> >
> > cmpxchg() with an immediate value could be replaced with less expensive
> > xchg(). The same true if new value don't _depend_ on the old one.
> >
> > In the second block, atomic_cmpxchg() return value isn't checked, so
> > after atomic_cmpxchg() -> atomic_xchg() conversion it could be replaced
> > with atomic_set(). Comparison with atomic_read() in the second chunk was
> > left as an optimisation (if that was the initial intention).
> >
> > Signed-off-by: Pavel Begunkov <[email protected]>
> > ---
> > lib/sbitmap.c | 10 +++-------
> > 1 file changed, 3 insertions(+), 7 deletions(-)
> >
> > diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> > index 155fe38756ec..7d7e0e278523 100644
> > --- a/lib/sbitmap.c
> > +++ b/lib/sbitmap.c
> > @@ -37,9 +37,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
> > /*
> > * First get a stable cleared mask, setting the old mask to 0.
> > */
> > - do {
> > - mask = sb->map[index].cleared;
> > - } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask);
> > + mask = xchg(&sb->map[index].cleared, 0);
This hunk is clearly correct.
> > /*
> > * Now clear the masked bits in our free word
> > @@ -527,10 +525,8 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
> > struct sbq_wait_state *ws = &sbq->ws[wake_index];
> >
> > if (waitqueue_active(&ws->wait)) {
> > - int o = atomic_read(&sbq->wake_index);
> > -
> > - if (wake_index != o)
> > - atomic_cmpxchg(&sbq->wake_index, o, wake_index);
> > + if (wake_index != atomic_read(&sbq->wake_index))
> > + atomic_set(&sbq->wake_index, wake_index);
This hunk used to imply a memory barrier and no longer does. I don't
think that's a problem, though.
Reviewed-by: Omar Sandoval <[email protected]>
On 5/23/19 9:39 AM, Pavel Begunkov (Silence) wrote:
> From: Pavel Begunkov <[email protected]>
>
> cmpxchg() with an immediate value could be replaced with less expensive
> xchg(). The same true if new value don't _depend_ on the old one.
>
> In the second block, atomic_cmpxchg() return value isn't checked, so
> after atomic_cmpxchg() -> atomic_xchg() conversion it could be replaced
> with atomic_set(). Comparison with atomic_read() in the second chunk was
> left as an optimisation (if that was the initial intention).
Applied, thanks.
--
Jens Axboe