From d9bf0b508ddfe19883b982b29a03c02ccbf53806 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Thu, 13 Jan 2011 19:59:47 +0000 Subject: [PATCH] dm io: remove BIO_RW_SYNCIO flag from kcopyd Remove the REQ_SYNC flag to improve write throughput 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 Signed-off-by: Mike Snitzer Signed-off-by: Alasdair G Kergon --- drivers/md/dm-kcopyd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c index d8587bac5682..5ad9231c8700 100644 --- a/drivers/md/dm-kcopyd.c +++ b/drivers/md/dm-kcopyd.c @@ -345,7 +345,7 @@ static int run_io_job(struct kcopyd_job *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,