Messages in this thread | | | Date | Thu, 23 Oct 2008 15:40:18 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH 1/2] libata: get rid of ATA_MAX_QUEUE loop in ata_qc_complete_multiple() |
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On Thu, Oct 23 2008, Jens Axboe wrote: > On Thu, Oct 23 2008, Tejun Heo wrote: > > 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; > > } > > That doesn't work (you're adding next to tag twice), it needs a little > tweak: > > while (done_mask) { > struct ata_queued_cmd *qc; > unsigned int next = __ffs(done_mask); > > if ((qc = ata_qc_from_tag(ap, tag + next))) { > ata_qc_complete(qc); > nr_done++; > } > next++; > tag += next; > done_mask >>= next; > } > > and I think it should work. Not tested yet :-)
Pondered some more, and it can't work. The problem is that if we complete tag 31, we attempt to shift done_mask down by 32 bits. On a 32-bit arch, that's not defined. So we DO need a check like the existing one, or something similar.
So I don't think we need to make changes to this patch either, at least unless one of you can come up with a better check that avoids a branch.
-- Jens Axboe
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