From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3015C433E0 for ; Wed, 27 Jan 2021 06:33:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9A46D20679 for ; Wed, 27 Jan 2021 06:33:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232034AbhA0Gcm (ORCPT ); Wed, 27 Jan 2021 01:32:42 -0500 Received: from m97179.mail.qiye.163.com ([220.181.97.179]:41140 "EHLO m97179.mail.qiye.163.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233793AbhA0DMj (ORCPT ); Tue, 26 Jan 2021 22:12:39 -0500 Received: from localhost.localdomain (unknown [218.94.118.90]) by m97179.mail.qiye.163.com (Hmail) with ESMTPA id 926D7E02834; Wed, 27 Jan 2021 11:11:14 +0800 (CST) From: Dongsheng Yang To: colyli@suse.de, linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, mchristi@redhat.com Cc: Dongsheng Yang Subject: [PATCH V2] bcache: dont reset bio opf in bch_data_insert_start Date: Wed, 27 Jan 2021 11:11:11 +0800 Message-Id: <20210127031111.3493-1-dongsheng.yang@easystack.cn> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-HM-Spam-Status: e1kfGhgUHx5ZQUtXWQgYFAkeWUFZS1VLWVdZKFlBSUI3V1ktWUFJV1kPCR oVCBIfWUFZGkgZGExDSR1KHkkaVkpNSkpMSkxLTE9DT05VGRETFhoSFyQUDg9ZV1kWGg8SFR0UWU FZT0tIVUpKS0hNSlVLWQY+ X-HM-Sender-Digest: e1kMHhlZQR0aFwgeV1kSHx4VD1lBWUc6MAg6Sjo6HD0zNghMGgIxHigq Pi4aCh5VSlVKTUpKTEpMS0xOS0hNVTMWGhIXVR8UFRwIEx4VHFUCGhUcOx4aCAIIDxoYEFUYFUVZ V1kSC1lBWUlKQ1VCT1VKSkNVQktZV1kIAVlBSE5KTDcG X-HM-Tid: 0a7741d2df4320bdkuqy926d7e02834 Precedence: bulk List-ID: X-Mailing-List: linux-bcache@vger.kernel.org commit ad0d9e76(bcache: use bio op accessors) makes the bi_opf modified by bio_set_op_attrs(). But there is a logical problem in this commit: trace_bcache_cache_insert(k); bch_keylist_push(&op->insert_keys); - n->bi_rw |= REQ_WRITE; + bio_set_op_attrs(n, REQ_OP_WRITE, 0); bch_submit_bbio(n, op->c, k, 0); } while (n != bio); The old code add REQ_WRITE into bio n and keep other flags; the new code set REQ_OP_WRITE to bi_opf, but reset all other flags. This problem is discoverd in our performance testing: (1) start a fio with 1M x 128depth for read in /dev/nvme0n1p1 (2) start a fio with 1M x 128depth for write in /dev/escache0 (cache device is /dev/nvme0n1p2) We found the BW of reading is 2000+M/s, but the BW of writing is 0-100M/s. After some debugging, we found the problem is io submit in writting is very slow. bch_data_insert_start() insert a bio to /dev/nvme0n1p1, but as cached_dev submit stack bio will be added into current->bio_list, and return.Then __submit_bio_noacct() will submit the new bio in bio_list into /dev/nvme0n1p1. This operation would be slow in blk_mq_submit_bio() -> rq_qos_throttle(q, bio); The rq_qos_throttle() will call wbt_should_throttle(), static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio) { switch (bio_op(bio)) { case REQ_OP_WRITE: /* * Don't throttle WRITE_ODIRECT */ if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE)) return false; ... ... } As the bio_set_op_attrs() reset the (REQ_SYNC | REQ_IDLE), so this write bio will be considered as non-direct write. After this fix, bio to nvme will flaged as (REQ_SYNC | REQ_IDLE), then fio for writing will get about 1000M/s bandwidth. Fixes: ad0d9e76a412 ("bcache: use bio op accessors") Close: EAS-60259 CC: Mike Christie Signed-off-by: Dongsheng Yang --- drivers/md/bcache/request.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c index c7cadaafa947..eb734f7ddaac 100644 --- a/drivers/md/bcache/request.c +++ b/drivers/md/bcache/request.c @@ -244,7 +244,7 @@ static void bch_data_insert_start(struct closure *cl) trace_bcache_cache_insert(k); bch_keylist_push(&op->insert_keys); - bio_set_op_attrs(n, REQ_OP_WRITE, 0); + n->bi_opf |= REQ_OP_WRITE; bch_submit_bbio(n, op->c, k, 0); } while (n != bio); -- 2.25.1