From 50d24c34403c62ad29e8b6db559d491bae20b4b7 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Thu, 3 Nov 2016 17:03:53 -0700 Subject: [PATCH] block: immediately dispatch big size request Currently block plug holds up to 16 non-mergeable requests. This makes sense if the request size is small, eg, reduce lock contention. But if request size is big enough, we don't need to worry about lock contention. Holding such request makes no sense and it lows the disk utilization. In practice, this improves 10% throughput for my raid5 sequential write workload. The size (128k) is arbitrary right now, but it makes sure lock contention is small. This probably could be more intelligent, eg, check average request size holded. Since this is mainly for sequential IO, probably not worthy. V2: check the last request instead of the first request, so as long as there is one big size request we flush the plug. Signed-off-by: Shaohua Li Signed-off-by: Jens Axboe --- block/blk-core.c | 4 +++- include/linux/blkdev.h | 1 + 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/block/blk-core.c b/block/blk-core.c index 0bfaa54d3e9f..2deca48a4a05 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1746,7 +1746,9 @@ get_rq: if (!request_count) trace_block_plug(q); else { - if (request_count >= BLK_MAX_REQUEST_COUNT) { + struct request *last = list_entry_rq(plug->list.prev); + if (request_count >= BLK_MAX_REQUEST_COUNT || + blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE) { blk_flush_plug_list(plug, false); trace_block_plug(q); } diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 13d893a69b46..9189a2d5c392 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1173,6 +1173,7 @@ struct blk_plug { struct list_head cb_list; /* md requires an unplug callback */ }; #define BLK_MAX_REQUEST_COUNT 16 +#define BLK_PLUG_FLUSH_SIZE (128 * 1024) struct blk_plug_cb; typedef void (*blk_plug_cb_fn)(struct blk_plug_cb *, bool); -- 2.20.1