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authorVivek Goyal <vgoyal@redhat.com>2009-11-26 09:45:40 +0100
committerJens Axboe <jens.axboe@oracle.com>2009-11-26 09:46:46 +0100
commitd9449ce35a1e8fb58dd2d419f9215562a14ecca0 (patch)
tree322f88901d3e494134354dcd5b7f63fa723145e8 /fs/direct-io.c
parentc16632bab1a17e357cec66920ceb3f0630009360 (diff)
downloadvexpress-lsk-d9449ce35a1e8fb58dd2d419f9215562a14ecca0.tar.gz
Fix regression in direct writes performance due to WRITE_ODIRECT flag removal
There seems to be a regression in direct write path due to following commit in for-2.6.33 branch of block tree. commit 1af60fbd759d31f565552fea315c2033947cfbe6 Author: Jeff Moyer <jmoyer@redhat.com> Date: Fri Oct 2 18:56:53 2009 -0400 block: get rid of the WRITE_ODIRECT flag Marking direct writes as WRITE_SYNC_PLUG instead of WRITE_ODIRECT, sets the NOIDLE flag in bio and hence in request. This tells CFQ to not expect more request from the queue and not idle on it (despite the fact that queue's think time is less and it is not seeky). So direct writers lose big time when competing with sequential readers. Using fio, I have run one direct writer and two sequential readers and following are the results with 2.6.32-rc7 kernel and with for-2.6.33 branch. Test ==== 1 direct writer and 2 sequential reader running simultaneously. [global] directory=/mnt/sdc/fio/ runtime=10 [seqwrite] rw=write size=4G direct=1 [seqread] rw=read size=2G numjobs=2 2.6.32-rc7 ========== direct writes: aggrb=2,968KB/s readers : aggrb=101MB/s for-2.6.33 branch ================= direct write: aggrb=19KB/s readers aggrb=137MB/s This patch brings back the WRITE_ODIRECT flag, with the difference that we don't set the BIO_RW_UNPLUG flag so that device is not unplugged after submission of request and an explicit unplug from submitter is required. That way we fix the jeff's issue of not enough merging taking place in aio path as well as make sure direct writes get their fair share. After the fix ============= for-2.6.33 + fix ---------------- direct writes: aggrb=2,728KB/s reads: aggrb=103MB/s Thanks Vivek Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'fs/direct-io.c')
-rw-r--r--fs/direct-io.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 3af761c8c5c..b912270942f 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1124,7 +1124,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
int acquire_i_mutex = 0;
if (rw & WRITE)
- rw = WRITE_SYNC_PLUG;
+ rw = WRITE_ODIRECT_PLUG;
if (bdev)
bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev));