On Fri, Sep 17, 2021 at 05:04:44PM -0700, Bart Van Assche wrote:
> Conditional statements are faster than indirect calls. Use a member variable
> to track the SCSI command submitter such that later patches can call
> scsi_done(scmd) instead of scmd->scsi_done(scmd).
>
> The asymmetric behavior that scsi_send_eh_cmnd() sets the submission
> context to the SCSI error handler and that it does not restore the
> submission context to the SCSI core is retained.
>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> drivers/scsi/scsi_error.c | 18 +++++++-----------
> drivers/scsi/scsi_lib.c | 9 +++++++++
> drivers/scsi/scsi_priv.h | 1 +
> include/scsi/scsi_cmnd.h | 7 +++++++
> 4 files changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 572673873ddf..ba6d748a0246 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1577,6 +1577,15 @@ static blk_status_t scsi_prepare_cmd(struct request *req)
>
> static void scsi_mq_done(struct scsi_cmnd *cmd)
> {
> + switch (cmd->submitter) {
> + case BLOCK_LAYER:
> + break;
> + case SCSI_ERROR_HANDLER:
> + return scsi_eh_done(cmd);
> + case SCSI_RESET_IOCTL:
> + return;
> + }
> +
Hmm, I'm confused, you replace one kind of branch with different one. Why
would that increase IOPS by 5%?
Maybe its because the new `submitter` field in `struct scsi_cmnd` is now
on a hot cache line, whereas `*scsi_done` is not?
--
Best Regards, Benjamin Block / Linux on IBM Z Kernel Development / IBM Systems
IBM Deutschland Research & Development GmbH / https://www.ibm.com/privacy
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