[PATCH] blk: don't account discard request size

[Shaohua Li]

In a workload with discard request, the IO throughput is generally much
higher than expected. This is quite confusing checking iostat. Discard
request doesn't really write data to drive, so don't account it.

Signed-off-by: Shaohua Li <shli@xxxxxx>
---
 block/blk-core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index fd154b9..0128d18 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2138,7 +2138,11 @@ EXPORT_SYMBOL_GPL(blk_rq_err_bytes);
 
 void blk_account_io_completion(struct request *req, unsigned int bytes)
 {
-	if (blk_do_io_stat(req)) {
+	/*
+	 * discard request doesn't really write @bytes to drive,
+	 * doesn't account it
+	 **/
+	if (blk_do_io_stat(req) && !(req->cmd_flags & REQ_DISCARD)) {
 		const int rw = rq_data_dir(req);
 		struct hd_struct *part;
 		int cpu;
-- 
1.8.1

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