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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 8DD53C433E6 for ; Tue, 26 Jan 2021 12:19:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 525E62223D for ; Tue, 26 Jan 2021 12:19:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404939AbhAZLE7 (ORCPT ); Tue, 26 Jan 2021 06:04:59 -0500 Received: from mx2.suse.de ([195.135.220.15]:45500 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726822AbhAZEe5 (ORCPT ); Mon, 25 Jan 2021 23:34:57 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 3948AAD78; Tue, 26 Jan 2021 04:34:15 +0000 (UTC) Subject: Re: [PATCH] bcache: dont reset bio opf in bch_data_insert_start To: Dongsheng Yang References: <20210125042942.1087170-1-dongsheng.yang@easystack.cn> <7569abf3-3e54-986e-8307-751fa5e00828@suse.de> <17578d50-4113-8f25-827e-840fafb09d6f@easystack.cn> Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, mchristi@redhat.com From: Coly Li Message-ID: <92c66f2d-22af-abd7-6fcb-ad896185c0c6@suse.de> Date: Tue, 26 Jan 2021 12:34:12 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <17578d50-4113-8f25-827e-840fafb09d6f@easystack.cn> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/26/21 12:32 PM, Dongsheng Yang wrote: > > 在 2021/1/25 星期一 下午 12:53, Coly Li 写道: >> On 1/25/21 12:29 PM, Dongsheng Yang wrote: >>> 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: ad0d9e76a4124708dddd00c04fc4b56fc86c02d6 >> It should be, >> Fixes: ad0d9e76a412 ("bcache: use bio op accessors") >> >>> Signed-off-by: Dongsheng Yang >> Please CC the fixed patch author  Mike Christie. > > > Hi Coly, > >     Should I send a V2 for commit message update? > > Or you can help to fix it when you take it from maillist? > Yes, please fix it in v2 version. And let's wait for response from Mike, maybe he has better suggestion to fix. Thanks. Coly Li