Commit cd464d83 authored Jan 15, 2019 by Bart Van Assche Committed by Martin K. Petersen Jan 22, 2019

scsi: core: Remove an atomic instruction from the hot path



From scsi_init_command(), a function called by scsi_mq_prep_fn():

	/* zero out the cmd, except for the embedded scsi_request */
	memset((char *)cmd + sizeof(cmd->req), 0,
		sizeof(*cmd) - sizeof(cmd->req) + dev->host->hostt->cmd_size);

In other words, scsi_mq_prep_fn() clears scsi_cmnd.flags. Hence move the
clear_bit() call into the else branch, the only branch in which this code
is necessary.

See also commit f1342709 ("scsi: Do not rely on blk-mq for double
completions").

Cc: Keith Busch <keith.busch@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

parent cf64e5a5

drivers/scsi/scsi_lib.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1712,13 +1712,13 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
		if (!scsi_host_queue_ready(q, shost, sdev))
		goto out_dec_target_busy;

		clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
		if (!(req->rq_flags & RQF_DONTPREP)) {
		ret = scsi_mq_prep_fn(req);
		if (ret != BLK_STS_OK)
		goto out_dec_host_busy;
		req->rq_flags \|= RQF_DONTPREP;
		} else {
		clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
		blk_mq_start_request(req);
		}

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