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SubjectRe: [PATCH 01/28] blk_end_request: add new request completion interface (take 3)
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Hi Boaz,

On Tue, 04 Dec 2007 15:56:32 +0200, Boaz Harrosh <bharrosh@panasas.com> wrote:
> > +int blk_end_request(struct request *rq, int uptodate, int nr_bytes)
> > +{
> > + struct request_queue *q = rq->q;
> > + unsigned long flags = 0UL;
> > +
> > + if (blk_fs_request(rq) || blk_pc_request(rq)) {
> > + if (__end_that_request_first(rq, uptodate, nr_bytes))
> > + return 1;
> > + }
> > +
> > + add_disk_randomness(rq->rq_disk);
> > +
> > + spin_lock_irqsave(q->queue_lock, flags);
> > + complete_request(rq, uptodate);
> > + spin_unlock_irqrestore(q->queue_lock, flags);
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(blk_end_request);
> > +
> > +/**
> > + * __blk_end_request - Helper function for drivers to complete the request.
> > + *
> > + * Description:
> > + * Must be called with queue lock held unlike blk_end_request().
> > + **/
> > +int __blk_end_request(struct request *rq, int uptodate, int nr_bytes)
> > +{
> > + if (blk_fs_request(rq) || blk_pc_request(rq)) {
> > + if (__end_that_request_first(rq, uptodate, nr_bytes))
> > + return 1;
> > + }
> > +
> > + add_disk_randomness(rq->rq_disk);
> > +
> > + complete_request(rq, uptodate);
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(__blk_end_request);
>
> I don't like it that you have two Identical but slightly different
> implementations I wish you would do an internal-with-flags
> implementation and then API ones can call the internal one. Or maybe
> just hold the spin_lock just a bit longer and have one call the other.
> To prove my case see how hard it is to add new code like with
> the bidi patch, where you need to add exact same code in 3 places.
> (OK only 2 places actually, if _callback is gone)

As for the internal-with-flags implementation, I once proposed
something like below but it was rejected by Jens.
(http://marc.info/?l=linux-kernel&m=118880584720600&w=2)
----------------------------------------------------------------------
static int internal_function(rq, needlock)
{
end_that_request_chunk(rq);
if (needlock)
spin_lock_irqsave();
end_that_request_last(rq);
if (needlock)
spin_unlock_irqrestore();
}
int blk_end_request(rq)
{
return internal_function(rq, 1);
}
int __blk_end_request(rq)
{
return internal_function(rq, 0);
}
----------------------------------------------------------------------

As for the holding-queue-lock-longer implementation,
end_that_request_chunk() completes bios in the request and it can
reaches filesystem layer and may take time.
I guess many drivers like scsi are calling end_that_request_chunk()
without queue's lock because of the reason above.

I'll try to remove the duplication again by another patch-set
after blk_end_request interfaces are merged.
So I would like to leave the duplication for now.
Is it acceptable for you?

Thanks,
Kiyoshi Ueda


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