From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Removing the REQ_SYNC flag improves write throughput twice when writing
to the origin with a snapshot on the same device (using the CFQ I/O
scheduler).
Sequential write throughput (chunksize of 4k, 32k, 512k)
unpatched: 8.5, 8.6, 9.3 MB/s
patched: 15.2, 18.5, 17.5 MB/s
Snapshot exception reallocations are triggered by writes that are
usually async, so mark the associated dm_io_request as async as well.
This helps when using the CFQ I/O scheduler because it has separate
queues for sync and async I/O, async is optimized for throughput, sync
for latency. With this change we're consciously favoring throughput
over latency.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
drivers/md/dm-kcopyd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
v2: updated patch header
Index: linux-2.6.36-rc7-fast/drivers/md/dm-kcopyd.c
===================================================================
--- linux-2.6.36-rc7-fast.orig/drivers/md/dm-kcopyd.c 2010-10-07 16:09:13.000000000 +0200
+++ linux-2.6.36-rc7-fast/drivers/md/dm-kcopyd.c 2010-10-15 03:18:52.000000000 +0200
@@ -345,7 +345,7 @@ static int run_io_job(struct kcopyd_job
{
int r;
struct dm_io_request io_req = {
- .bi_rw = job->rw | REQ_SYNC | REQ_UNPLUG,
+ .bi_rw = job->rw | REQ_UNPLUG,
.mem.type = DM_IO_PAGE_LIST,
.mem.ptr.pl = job->pages,
.mem.offset = job->offset,
--
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