Messages in this thread |  | | | Date | Sun, 20 Jul 2008 10:23:02 -0700 (PDT) | | Subject | Re: [PATCH] block: fix q->max_segment_size checking in blk_recalc_rq_segments about VMERGE | | From | David Miller <> |
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From: James Bottomley <James.Bottomley@HansenPartnership.com> Date: Sun, 20 Jul 2008 09:52:25 -0500
> Since we're using it successfully in parisc, I don't want the block code > removed, but I don't see a reason to force other architectures to use > it. > > However, it has two use cases. One is the legacy one of making rather > dumb I/O cards perform better (which is the primary on on parisc), but > there is a current one making huge transfers go through SCSI using using > the sg_table code. That latter is pretty vital to me since I have to > keep the code working, but I don't really have any SCSI cards that can > take advantage of it without virtual merging. As a slight irony, IBM is > trying to persuade me that a ppc would be better than a parisc for big > endian I/O testing ... so I might just be seeing if I can make virtual > merging work on power too.
All of this is gibberish, we've been over this a few times already in this thread.
For a dumb I/O card, you advertise SG_ALL capabilities, the IOMMU is going to merge things as it would have anyways, and you have code in the driver to advance SG entries after each "dumb I/O".
There is zero value to the vmerge code, the real gains are being realized already.
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