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[SCSI] libosd: osd_req_read_sg, optimize the single entry case

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Since sg-read is a bidi operation, it is a gain to convert
a single sg entry into a regular read. Better do this in the
generic layer then force each caller to do so.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
This commit is contained in:
Boaz Harrosh 2011-01-23 17:53:24 +02:00 committed by James Bottomley
parent 1e34c83873
commit 4977c82504
1 changed files with 16 additions and 4 deletions
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20
drivers/scsi/osd/osd_initiator.c
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@ -1005,11 +1005,23 @@ int osd_req_read_sg(struct osd_request *or,
const struct osd_sg_entry *sglist, unsigned numentries) const struct osd_sg_entry *sglist, unsigned numentries)
{ {
u64 len; u64 len;
int ret = _add_sg_continuation_descriptor(or, sglist, numentries, &len); u64 off;
int ret;
if (ret) if (numentries > 1) {
return ret; off = 0;
osd_req_read(or, obj, 0, bio, len); ret = _add_sg_continuation_descriptor(or, sglist, numentries,
&len);
if (ret)
return ret;
} else {
/* Optimize the case of single segment, read_sg is a
* bidi operation.
*/
len = sglist->len;
off = sglist->offset;
}
osd_req_read(or, obj, off, bio, len);
return 0; return 0;
} }