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| author | Mikulas Patocka <mpatocka@redhat.com> | 2010-08-12 05:14:02 +0200 |
|---|---|---|
| committer | Alasdair G Kergon <agk@redhat.com> | 2010-08-12 05:14:02 +0200 |
| commit | b1d5552838334c600b068c9c8cc18638e5a8cb47 (patch) | |
| tree | 789e435ab60e6956abffc15b4da85fe1e5b1714c /drivers/md/dm.h | |
| parent | dm: do not initialise full request queue when bio based (diff) | |
| download | linux-b1d5552838334c600b068c9c8cc18638e5a8cb47.tar.xz linux-b1d5552838334c600b068c9c8cc18638e5a8cb47.zip | |
dm snapshot: implement merge
Implement merge method for the snapshot origin to improve read
performance.
Without merge method, dm asks the upper layers to submit smallest possible
bios --- one page. Submitting such small bios impacts performance negatively
when reading or writing the origin device.
Without this patch, CPU consumption when reading the origin on lvm on md-raid0
was 6 to 12%, with this patch, it drops to 1 to 4%.
Note: in my testing, it actually degraded performance in some settings, I
traced it to Maxtor disks having problems with > 512-sector requests.
Reducing the number of sectors to /sys/block/sd*/queue/max_sectors_kb to
256 fixed the read performance. I think we don't have to care about weird
disks that actually degrade performance because of large requests being
sent to them.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'drivers/md/dm.h')
0 files changed, 0 insertions, 0 deletions