* [RFC] block: change to use atomic_inc_return_release()
@ 2015-11-17 3:24 yalin wang
2015-11-17 3:38 ` Jens Axboe
0 siblings, 1 reply; 3+ messages in thread
From: yalin wang @ 2015-11-17 3:24 UTC (permalink / raw)
To: axboe, linux-kernel; +Cc: yalin wang
Some arch define this atomic_inc_return_release() OP.
Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
---
block/bio.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index fbc558b..b251857 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -310,8 +310,7 @@ static void bio_chain_endio(struct bio *bio, int error)
static inline void bio_inc_remaining(struct bio *bio)
{
bio->bi_flags |= (1 << BIO_CHAIN);
- smp_mb__before_atomic();
- atomic_inc(&bio->__bi_remaining);
+ atomic_inc_return_release(&bio->__bi_remaining);
}
/**
--
1.9.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [RFC] block: change to use atomic_inc_return_release()
2015-11-17 3:24 [RFC] block: change to use atomic_inc_return_release() yalin wang
@ 2015-11-17 3:38 ` Jens Axboe
2015-11-17 4:11 ` yalin wang
0 siblings, 1 reply; 3+ messages in thread
From: Jens Axboe @ 2015-11-17 3:38 UTC (permalink / raw)
To: yalin wang, linux-kernel
On 11/16/2015 08:24 PM, yalin wang wrote:
> Some arch define this atomic_inc_return_release() OP.
That is a very vague commit message, you'll need a whole lot more than
that... A commit message is supposed to describe the reason for the
change. You provide no reason for the change.
> diff --git a/block/bio.c b/block/bio.c
> index fbc558b..b251857 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -310,8 +310,7 @@ static void bio_chain_endio(struct bio *bio, int error)
> static inline void bio_inc_remaining(struct bio *bio)
> {
> bio->bi_flags |= (1 << BIO_CHAIN);
> - smp_mb__before_atomic();
> - atomic_inc(&bio->__bi_remaining);
> + atomic_inc_return_release(&bio->__bi_remaining);
Are these equivalent? Where's the documentation for this primitive? The
previous code ensured that we ordered the dec of the remaining count
with the update of the flags.
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC] block: change to use atomic_inc_return_release()
2015-11-17 3:38 ` Jens Axboe
@ 2015-11-17 4:11 ` yalin wang
0 siblings, 0 replies; 3+ messages in thread
From: yalin wang @ 2015-11-17 4:11 UTC (permalink / raw)
To: Jens Axboe; +Cc: linux-kernel
> On Nov 17, 2015, at 11:38, Jens Axboe <axboe@kernel.dk> wrote:
>
> On 11/16/2015 08:24 PM, yalin wang wrote:
>> Some arch define this atomic_inc_return_release() OP.
>
> That is a very vague commit message, you'll need a whole lot more than that... A commit message is supposed to describe the reason for the change. You provide no reason for the change.
>
>> diff --git a/block/bio.c b/block/bio.c
>> index fbc558b..b251857 100644
>> --- a/block/bio.c
>> +++ b/block/bio.c
>> @@ -310,8 +310,7 @@ static void bio_chain_endio(struct bio *bio, int error)
>> static inline void bio_inc_remaining(struct bio *bio)
>> {
>> bio->bi_flags |= (1 << BIO_CHAIN);
>> - smp_mb__before_atomic();
>> - atomic_inc(&bio->__bi_remaining);
>> + atomic_inc_return_release(&bio->__bi_remaining);
>
> Are these equivalent? Where's the documentation for this primitive? The previous code ensured that we ordered the dec of the remaining count with the update of the flags.
>
i just have a look at ARM64 implementation for this new atomic OP ,
but i don’t find doc in memory-barrier.txt . so i make this RFC for some response,
atomic_inc_return_release() should have store_release() class memory barriers .
in this example, smp_store_release() memory barrier is not enough ?
just make sure bi_flags update can been seen by other cores before update atomic counter.
atomic_inc_return_{release,acquire,relax} OP seems newly add to kernel .
But i don’t see much users in code .
Can it be used to replace lots of smp_mb__before_atomic() ?
Thanks
^ permalink raw reply [flat|nested] 3+ messages in thread
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2015-11-17 3:24 [RFC] block: change to use atomic_inc_return_release() yalin wang
2015-11-17 3:38 ` Jens Axboe
2015-11-17 4:11 ` yalin wang
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