On Sun, 2010-09-19 at 20:53 +0800, Hillf Danton wrote:
> It seems that check for host busy is deserved before scanning the starved list.
> And list operation is simplified.
>
> Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
> ---
>
> --- o/linux-2.6.36-rc4/drivers/scsi/scsi_lib.c 2010-09-13
> 07:07:38.000000000 +0800
> +++ m/linux-2.6.36-rc4/drivers/scsi/scsi_lib.c 2010-09-19
> 20:32:34.000000000 +0800
> @@ -399,18 +399,20 @@ static inline int scsi_host_is_busy(stru
> */
> static void scsi_run_queue(struct request_queue *q)
> {
> - struct scsi_device *sdev = q->queuedata;
> + struct scsi_device *sdev = q->queuedata, *safe;
> struct Scsi_Host *shost = sdev->host;
> - LIST_HEAD(starved_list);
> unsigned long flags;
>
> if (scsi_target(sdev)->single_lun)
> scsi_single_lun_run(sdev);
>
> spin_lock_irqsave(shost->host_lock, flags);
> - list_splice_init(&shost->starved_list, &starved_list);
> -
> - while (!list_empty(&starved_list)) {
> + if (scsi_host_is_busy(shost)) {
> + spin_unlock_irqrestore(shost->host_lock, flags);
> + return;
> + }
To be honest, there's no real gain from this micro-optimisation.
> + list_for_each_entry_safe(sdev, safe, &shost->starved_list,
> + starved_entry) {
And this is definitely wrong. The list is altered in flight so the
whole purpose of the static copy is to process only what existed before
we began; otherwise you can get a livelock.
James
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