Jeff Garzik wrote:
Mark Lord wrote:
Jens / Jeff,
Each libata driver registers a .dma_boundary field with SCSI.
This field is used to prevent merging of bio segments across
a hardware limitation boundary, usually 0xffff.
This looks like it works for regular block I/O,
but I'm not so sure about SGIO originated requests.
Any thoughts, or code you can point me to?
Everything goes through the block layer, including SG_IO, so everyone
agrees on the boundaries that must be respected.
scsi sets blk_queue_segment_boundary() then gets out of the way, for the
most part. BIOVEC_SEG_BOUNDARY() is the macro that accesses this. Trace
back and forth from there. You will probably run into a call to
blk_recount_segments() in __bio_add_page(), or maybe you'll check the
seg boundary from another path.
Yeah, I'm familiar with that part, and thanks for the note about SGIO.
So therefore, code to manage the dma_boundary is NOT necessary in sata drivers.
Right? Currently we have in sata_mv.c:
MV_DMA_BOUNDARY = 0xffff;
while (sg_len) {
offset = addr & MV_DMA_BOUNDARY;
len = sg_len;
if ((offset + sg_len) > 0x10000)
len = 0x10000 - offset;
...
That whole block should be able to go, then.
Cheers
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