Messages in this thread | | | Subject | Re: [RFC] block: change to use atomic_inc_return_release() | From | yalin wang <> | Date | Tue, 17 Nov 2015 12:11:10 +0800 |
| |
> 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
| |