Re: [PATCH] block: move SCSI timeout check into block

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2008-12-17 at 09:06 +0100, Jens Axboe wrote:
> On Tue, Dec 16 2008, James Bottomley wrote:
> > We can eliminate the SCSI command timed out check entirely if the block
> > layer does this for us.  The way to do this in block is to check how
> > long the request has been outstanding if a requeue is requested and
> > ending it if we've gone over retries * timeout.
> > 
> > This will also eliminate many cases in SCSI where we evade the command
> > timeout for various reasons (like initial success converted to requeue)
> > 
> > James
> > 
> > ---
> > 
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index c36aa98..d32af31 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -926,6 +926,8 @@ EXPORT_SYMBOL(blk_start_queueing);
> >   */
> >  void blk_requeue_request(struct request_queue *q, struct request *rq)
> >  {
> > +	unsigned long wait_for = (rq->retries + 1) * rq->timeout;
> > +
> >  	blk_delete_timer(rq);
> >  	blk_clear_rq_complete(rq);
> >  	blk_add_trace_rq(q, rq, BLK_TA_REQUEUE);
> > @@ -933,7 +935,17 @@ void blk_requeue_request(struct request_queue *q, struct request *rq)
> >  	if (blk_rq_tagged(rq))
> >  		blk_queue_end_tag(q, rq);
> >  
> > -	elv_requeue_request(q, rq);
> > +	if (time_before(rq->start_time + wait_for, jiffies)) {
> 
> I prefer time_after(), reads better.
> 
> > +		int bytes = (rq->hard_nr_sectors << 9);
> > +
> > +		printk(KERN_ERR "%s: timing out command, waited %lus\n",
> > +		       rq->rq_disk ? rq->rq_disk->disk_name : "?",
> > +		       wait_for/HZ);
> > +		if (blk_pc_request(rq))
> > +			bytes = rq->data_len;
> > +		blk_end_request(rq, -EIO, bytes);
> 
> You can just do
> 
>                 blk_end_request(rq, -EIO, blk_rq_bytes(rq));
> 
> and get rid of the 'bytes' variable and type check.
> 
> > +	} else
> > +		elv_requeue_request(q, rq);
> >  }
> >  EXPORT_SYMBOL(blk_requeue_request);
> 
> But I agree with the patch. Will you rediff, or shall I just apply with
> the suggest changes?

I'll rediff ... we're going to have to test it out quite a bit,
especially when I pull the SCSI timeout stuff.

James