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SubjectRe: [PATCH 1/2] libata: get rid of ATA_MAX_QUEUE loop in ata_qc_complete_multiple()
On Thu, Oct 23 2008, Tejun Heo wrote:
> Jens Axboe wrote:
> > @@ -4811,16 +4811,19 @@ int ata_qc_complete_multiple(struct ata_port *ap, u32 qc_active)
> > return -EINVAL;
> > }
> >
> > - for (i = 0; i < ATA_MAX_QUEUE; i++) {
> > + while (done_mask) {
> > struct ata_queued_cmd *qc;
> > + unsigned int next = __ffs(done_mask);
> >
> > - if (!(done_mask & (1 << i)))
> > - continue;
> > -
> > - if ((qc = ata_qc_from_tag(ap, i))) {
> > + qc = ata_qc_from_tag(ap, i + next);
> > + if (qc) {
> > ata_qc_complete(qc);
> > nr_done++;
> > }
> > + if (++next >= ATA_MAX_QUEUE)
> > + break;
> > + i += next;
> > + done_mask >>= next;
>
> Shouldn't this be...
>
> i += next + 1;
> if (i >= ATA_MAX_QUEUE)
> break;
>
> or better...
>
> while (done_mask) {
> struct ata_queued_cmd *qc;
> unsigned int next = __ffs(done_mask);
>
> tag += next;
> if ((qc = ata_qc_from_tag(ap, tag))) {
> ata_qc_complete(qc);
> nr_done++;
> }
> next++;
> tag += next;
> done_mask >>= next;
> }
>
> done_mask is guaranteed to be zero at when tag reaches ATA_MAX_QUEUE.

That does indeed look a lot cleaner. I think it was rewritten at some
point and kept some of the logic for not passing 0 into __ffs, but it's
clearly pointless now.

I'll send out a revised patch when it's tested.

--
Jens Axboe



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