4.15-stable review patch. If anyone has any objections, please let me know.
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From: Jens Axboe axboe@kernel.dk
commit 5235553d821433e1f4fa720fd025d2c4b7ee9994 upstream.
Mikulas reported a workload that saw bad performance, and figured out what it was due to various other types of requests being accounted as reads. Flush requests, for instance. Due to the high latency of those, we heavily throttle the writes to keep the latencies in balance. But they really should be accounted as writes.
Fix this by checking the exact type of the request. If it's a read, account as a read, if it's a write or a flush, account as a write. Any other request we disregard. Previously everything would have been mistakenly accounted as reads.
Reported-by: Mikulas Patocka mpatocka@redhat.com Cc: stable@vger.kernel.org # v4.12+ Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- block/blk-wbt.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -697,7 +697,15 @@ u64 wbt_default_latency_nsec(struct requ
static int wbt_data_dir(const struct request *rq) { - return rq_data_dir(rq); + const int op = req_op(rq); + + if (op == REQ_OP_READ) + return READ; + else if (op == REQ_OP_WRITE || op == REQ_OP_FLUSH) + return WRITE; + + /* don't account */ + return -1; }
int wbt_init(struct request_queue *q)