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| author | Alexey Dobriyan | 2020-05-07 23:07:04 +0300 |
|---|---|---|
| committer | Jens Axboe | 2020-05-09 16:07:58 -0600 |
| commit | a8de6639169b90e3dc4f27e752a3c5abac5e90da (patch) | |
| tree | 8d8734baf42b3aaa451e54415fef1f799c8176d9 /block/bounce.c | |
| parent | 6bd87eec23cbc9ed222bed0f5b5b02bf300e9a8d (diff) | |
nvme-pci: fix "slimmer CQ head update"
Pre-incrementing ->cq_head can't be done in memory because OOB value
can be observed by another context.
This devalues space savings compared to original code :-\
$ ./scripts/bloat-o-meter ../vmlinux-000 ../obj/vmlinux
add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-32 (-32)
Function old new delta
nvme_poll_irqdisable 464 456 -8
nvme_poll 455 447 -8
nvme_irq 388 380 -8
nvme_dev_disable 955 947 -8
But the code is minimal now: one read for head, one read for q_depth,
one increment, one comparison, single instruction phase bit update and
one write for new head.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reported-by: John Garry <john.garry@huawei.com>
Tested-by: John Garry <john.garry@huawei.com>
Fixes: e2a366a4b0feaeb ("nvme-pci: slimmer CQ head update")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/bounce.c')
0 files changed, 0 insertions, 0 deletions