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Subject[patch 1/2]block: change force plug flush call order
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Do blk_flush_plug_list() first and then add new request at the tail. New
request can't be merged to existing requests, but later new requests might
be merged with this new one. If blk_flush_plug_list() is done later, the
merge doesn't happen.
Believe it or not, this fixes a 10% regression running sysbench workload.

Signed-off-by: Shaohua Li <shli@kernel.org>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
block/blk-core.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux/block/blk-core.c
===================================================================
--- linux.orig/block/blk-core.c 2011-08-24 16:09:39.000000000 +0800
+++ linux/block/blk-core.c 2011-08-24 16:13:20.000000000 +0800
@@ -1302,11 +1302,11 @@ get_rq:
if (__rq->q != q)
plug->should_sort = 1;
}
- list_add_tail(&req->queuelist, &plug->list);
- plug->count++;
- drive_stat_acct(req, 1);
if (plug->count >= BLK_MAX_REQUEST_COUNT)
blk_flush_plug_list(plug, false);
+ plug->count++;
+ list_add_tail(&req->queuelist, &plug->list);
+ drive_stat_acct(req, 1);
} else {
spin_lock_irq(q->queue_lock);
add_acct_request(q, req, where);



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