Hi James, On Fri, 03 Oct 2008 16:51:46 -0500, James Bottomley wrote: > On Fri, 2008-10-03 at 16:06 -0400, Kiyoshi Ueda wrote: > > Hi James, > > > > On Fri, 03 Oct 2008 13:14:56 -0500, James Bottomley wrote: > > > On Wed, 2008-10-01 at 14:50 -0400, Kiyoshi Ueda wrote: > > > > Hi James, > > > > > > > > I hope the previous RFC patch(*) would be no problem, since I haven't > > > > gotten any negative comment. > > > > (*) http://lkml.org/lkml/2008/9/25/262 > > > > > > > > So could you take this patch for 2.6.28 additionally? > > > > This patch implements a new interface of the block layer for > > > > request stacking drivers. > > > > There should be no effect on existing drivers' behavior. > > > > > > > > This patch was created on top of the commit below of scsi-post-merge-2.6. > > > > --------------------------------------------------------------------- > > > > commit e49f03f37104c0e7cae7c455480069bada00932f > > > > Author: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> > > > > Date: Fri Sep 12 16:46:51 2008 -0500 > > > > > > > > [SCSI] scsi_error: fix target reset handling > > > > --------------------------------------------------------------------- > > > > > > > > And this patch depends on the following block layer patch, which > > > > is in Jens' for-2.6.28 of linux-2.6-block. > > > > http://lkml.org/lkml/2008/9/29/142 > > > > > > > > Thanks, > > > > Kiyoshi Ueda > > > > > > > > > > > > Subject: [PATCH 1/1] scsi: export busy state via q->lld_busy_fn() > > > > > > > > This patch implements q->lld_busy_fn() for scsi mid layer to export > > > > its busy state. > > > > > > > > Please note that it checks the cached information (sdev->lld_busy) > > > > for efficiency, instead of checking the actual state of > > > > sdev/starget/shost everytime. > > > > > > > > So the care must be taken not to leave sdev->lld_busy = 1 for > > > > the following cases: > > > > - when there is no request in the sdev queue > > > > - when scsi can't dispatch I/Os anymore and needs to kill I/Os > > > > Otherwise, request stacking drivers may not submit any request, > > > > and then, nobody sets back lld_busy = 0 and that causes deadlock. > > > > > > > > OTOH, it has no major problem in setting sdev->lld_busy = 0 even when > > > > the starget/shost is actually busy, because newly submitted request > > > > will soon turn it to 1 in scsi_request_fn(). > > > > > > > > > > > > Signed-off-by: Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx> > > > > Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx> > > > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > > > Cc: Mike Christie <michaelc@xxxxxxxxxxx> > > > > Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> > > > > --- > > > > drivers/scsi/scsi.c | 4 ++-- > > > > drivers/scsi/scsi_lib.c | 20 +++++++++++++++++++- > > > > include/scsi/scsi_device.h | 13 +++++++++++++ > > > > 3 files changed, 34 insertions(+), 3 deletions(-) > > > > > > > > Index: scsi-post-merge-2.6/drivers/scsi/scsi_lib.c > > > > =================================================================== > > > > --- scsi-post-merge-2.6.orig/drivers/scsi/scsi_lib.c > > > > +++ scsi-post-merge-2.6/drivers/scsi/scsi_lib.c > > > > @@ -480,6 +480,8 @@ void scsi_device_unbusy(struct scsi_devi > > > > spin_unlock(shost->host_lock); > > > > spin_lock(sdev->request_queue->queue_lock); > > > > sdev->device_busy--; > > > > + if (sdev->device_busy < sdev->queue_depth && !sdev->device_blocked) > > > > + sdev->lld_busy = 0; > > > > spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags); > > > > } > > > > > > > > @@ -1535,6 +1537,13 @@ static void scsi_softirq_done(struct req > > > > } > > > > } > > > > > > > > +static int scsi_lld_busy(struct request_queue *q) > > > > +{ > > > > + struct scsi_device *sdev = q->queuedata; > > > > + > > > > + return sdev ? sdev->lld_busy : 0; > > > > +} > > > > > > Since you've moved to a functional approach, why is this lld_busy flag > > > still necessary? Surely this function can just check the three blocked > > > conditions and the two overqueue ones at this point without ever having > > > to reach into any of the SCSI internals? > > > > This flag is not necessary for the functionality, it's for efficiency. > > I could take the "everytime checking" approach above, but I think > > caching the busy state into the flag is more efficient, since: > > > > - The check function will be called from request stacking drivers > > frequently (e.g. request-based dm calls it everytime before > > an request is dispatched from the dm device.) > > Hmm, well, so will the operations you've put into the stack, but for > every request, not just for stacked drivers. > > > - The scsi busy state checking needs queue lock and host lock > > even while the scsi busy state doesn't changed from the previous > > checking. > > You don't need the locks ... you don't care if the values change as you > read them because this is just heuristic. You do care that you get an > architectural guarantee that you read a consistent value (as in if the > variable is altering you read either the before or after) but this isn't > necessary as the algorithm is statistical: as long as it gets bogus > values infrequently the effects won't be noticeable different. Thank you for the good suggestion. I sent another patch-set: http://lkml.org/lkml/2008/10/4/85 Thanks, Kiyoshi Ueda -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
