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author | Uros Bizjak <ubizjak@gmail.com> | 2022-10-20 17:35:40 +0200 |
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committer | Christoph Hellwig <hch@lst.de> | 2022-11-15 10:49:48 +0100 |
commit | bbf5410bc69e131c82ad970ce7ee28b5906a6cc5 (patch) | |
tree | 93af6677b80cc96e9b3508f227e682d7d7b639a7 /drivers/nvme | |
parent | 5626196a5ae0937368b35c3625c428a2125b0f44 (diff) | |
download | linux-stable-bbf5410bc69e131c82ad970ce7ee28b5906a6cc5.tar.gz linux-stable-bbf5410bc69e131c82ad970ce7ee28b5906a6cc5.tar.bz2 linux-stable-bbf5410bc69e131c82ad970ce7ee28b5906a6cc5.zip |
nvmet: use try_cmpxchg in nvmet_update_sq_head
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
nvmet_update_sq_head. 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.
Note that the value from *ptr should be read using READ_ONCE to prevent
the compiler from merging, refetching or reordering the read.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'drivers/nvme')
-rw-r--r-- | drivers/nvme/target/core.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c index aecb5853f8da..560b6bbb6c44 100644 --- a/drivers/nvme/target/core.c +++ b/drivers/nvme/target/core.c @@ -695,11 +695,10 @@ static void nvmet_update_sq_head(struct nvmet_req *req) if (req->sq->size) { u32 old_sqhd, new_sqhd; + old_sqhd = READ_ONCE(req->sq->sqhd); do { - old_sqhd = req->sq->sqhd; new_sqhd = (old_sqhd + 1) % req->sq->size; - } while (cmpxchg(&req->sq->sqhd, old_sqhd, new_sqhd) != - old_sqhd); + } while (!try_cmpxchg(&req->sq->sqhd, &old_sqhd, new_sqhd)); } req->cqe->sq_head = cpu_to_le16(req->sq->sqhd & 0x0000FFFF); } |