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SubjectRe: [dm-devel] [PATCH 2/2] scsi: exports busy status via bdi_lld_congested
Kiyoshi Ueda wrote:
> This patch change scsi mid layer to export its busy status.
> Not set the busy flag, when scsi can't dispatch I/Os anymore and
> needs to kill I/Os. Otherwise, request stacking drivers may hold
> requests forever.
>
>
> Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
> ---
> drivers/scsi/scsi.c | 4 ++--
> drivers/scsi/scsi_lib.c | 23 ++++++++++++++++++++++-
> 2 files changed, 24 insertions(+), 3 deletions(-)
>
> Index: scsi-misc-2.6/drivers/scsi/scsi_lib.c
> ===================================================================
> --- scsi-misc-2.6.orig/drivers/scsi/scsi_lib.c
> +++ scsi-misc-2.6/drivers/scsi/scsi_lib.c
> @@ -459,17 +459,30 @@ static void scsi_init_cmd_errh(struct sc
>
> void scsi_device_unbusy(struct scsi_device *sdev)
> {
> + int host_congested;
> struct Scsi_Host *shost = sdev->host;
> unsigned long flags;
>
> spin_lock_irqsave(shost->host_lock, flags);
> shost->host_busy--;
> + if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
> + shost->host_blocked || shost->host_self_blocked ||
> + scsi_host_in_recovery(shost))
> + host_congested = 1;
> + else
> + host_congested = 0;
> +

You might want to check if the starget busy too (scsi-misc has this but
Jens's tree and linus do not)? The code below that I snipped from
scsi_request_fn will set the congested bits if scsi_target_queue_ready
returns 0, so above here you would want to clear it if it not congested
anymore.

> if (unlikely(scsi_host_in_recovery(shost) &&
> (shost->host_failed || shost->host_eh_scheduled)))
> scsi_eh_wakeup(shost);
> spin_unlock(shost->host_lock);
> +
> spin_lock(sdev->request_queue->queue_lock);
> sdev->device_busy--;
> + if (bdi_lld_congested(&sdev->request_queue->backing_dev_info) &&
> + !host_congested && sdev->device_busy < sdev->queue_depth &&
> + !sdev->device_blocked)
> + clear_bdi_lld_congested(&sdev->request_queue->backing_dev_info);
> spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
> }
>



> @@ -1593,6 +1613,7 @@ static void scsi_request_fn(struct reque
> * later time.
> */
> spin_lock_irq(q->queue_lock);
> + set_bdi_lld_congested(&q->backing_dev_info);
> blk_requeue_request(q, req);
> sdev->device_busy--;
> if(sdev->device_busy == 0)


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