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ublk: optimize UBLK_IO_UNREGISTER_IO_BUF on daemon task

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ublk_io_release() performs an expensive atomic refcount decrement. This
atomic operation is unnecessary in the common case where the request's
buffer is registered and unregistered on the daemon task before handling
UBLK_IO_COMMIT_AND_FETCH_REQ for the I/O. So if ublk_io_release() is
called on the daemon task and task_registered_buffers is positive, just
decrement task_registered_buffers (nonatomically). ublk_sub_req_ref()
will apply this decrement when it atomically subtracts from io->ref.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250620151008.3976463-13-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Caleb Sander Mateos 2025-06-20 09:10:06 -06:00 • committed by Jens Axboe
parent 8a8fe42d76
commit 1ceeedb597
1 changed files with 8 additions and 1 deletions
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9
drivers/block/ublk_drv.c
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@ -2030,7 +2030,14 @@ static void ublk_io_release(void *priv)
struct ublk_queue *ubq = rq->mq_hctx->driver_data;
struct ublk_io *io = &ubq->ios[rq->tag];
ublk_put_req_ref(ubq, io, rq);
/*
* task_registered_buffers may be 0 if buffers were registered off task
* but unregistered on task. Or after UBLK_IO_COMMIT_AND_FETCH_REQ.
*/
if (current == io->task && io->task_registered_buffers)
io->task_registered_buffers--;
else
ublk_put_req_ref(ubq, io, rq);
}
static int ublk_register_io_buf(struct io_uring_cmd *cmd,