lkml.org 
[lkml]   [2019]   [Jun]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/1] sbitmap: Replace cmpxchg with xchg
From
Date
Ping?

On 23/05/2019 08:39, Pavel Begunkov (Silence) wrote:
> From: Pavel Begunkov <asml.silence@gmail.com>
>
> 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 <asml.silence@gmail.com>
> ---
> 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

[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2019-06-29 17:43    [W:0.089 / U:23.560 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site