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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, 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 957E8C433E0 for ; Fri, 19 Mar 2021 08:00:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 561A264F69 for ; Fri, 19 Mar 2021 08:00:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234251AbhCSH7b (ORCPT ); Fri, 19 Mar 2021 03:59:31 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:58495 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234274AbhCSH7J (ORCPT ); Fri, 19 Mar 2021 03:59:09 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0USZNFva_1616140747; Received: from admindeMacBook-Pro-2.local(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0USZNFva_1616140747) by smtp.aliyun-inc.com(127.0.0.1); Fri, 19 Mar 2021 15:59:07 +0800 Subject: Re: [RFC PATCH V2 05/13] block: add req flag of REQ_TAG To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Mike Snitzer , dm-devel@redhat.com References: <20210318164827.1481133-1-ming.lei@redhat.com> <20210318164827.1481133-6-ming.lei@redhat.com> From: JeffleXu Message-ID: <50e454b9-2027-cf38-0be7-a4ecfdd54027@linux.alibaba.com> Date: Fri, 19 Mar 2021 15:59:06 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210318164827.1481133-6-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 3/19/21 12:48 AM, Ming Lei wrote: > Add one req flag REQ_TAG which will be used in the following patch for > supporting bio based IO polling. > > Exactly this flag can help us to do: > > 1) request flag is cloned in bio_fast_clone(), so if we mark one FS bio > as REQ_TAG, all bios cloned from this FS bio will be marked as REQ_TAG. > > 2)create per-task io polling context if the bio based queue supports polling > and the submitted bio is HIPRI. This per-task io polling context will be > created during submit_bio() before marking this HIPRI bio as REQ_TAG. Then > we can avoid to create such io polling context if one cloned bio with REQ_TAG > is submitted from another kernel context. > > 3) for supporting bio based io polling, we need to poll IOs from all > underlying queues of bio device/driver, this way help us to recognize which > IOs need to polled in bio based style, which will be implemented in next > patch. > > Signed-off-by: Ming Lei > --- > block/blk-core.c | 29 +++++++++++++++++++++++++++-- > include/linux/blk_types.h | 4 ++++ > 2 files changed, 31 insertions(+), 2 deletions(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index 0b00c21cbefb..efc7a61a84b4 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -840,11 +840,30 @@ static inline bool blk_queue_support_bio_poll(struct request_queue *q) > static inline void blk_bio_poll_preprocess(struct request_queue *q, > struct bio *bio) > { > + bool mq; > + > if (!(bio->bi_opf & REQ_HIPRI)) > return; > > - if (!blk_queue_poll(q) || (!queue_is_mq(q) && !blk_get_bio_poll_ctx())) > + /* > + * Can't support bio based IO poll without per-task poll queue > + * > + * Now we have created per-task io poll context, and mark this > + * bio as REQ_TAG, so: 1) if any cloned bio from this bio is > + * submitted from another kernel context, we won't create bio > + * poll context for it, so that bio will be completed by IRQ; > + * 2) If such bio is submitted from current context, we will > + * complete it via blk_poll(); 3) If driver knows that one > + * underlying bio allocated from driver is for FS bio, meantime > + * it is submitted in current context, driver can mark such bio > + * as REQ_TAG manually, so the bio can be completed via blk_poll > + * too. > + */ Sorry I can't understand case 3, could you please further explain it? If 'driver marks such bio as REQ_TAG manually', then per-task io poll context won't be created, and thus REQ_HIPRI will be cleared, in which case the bio will be completed by IRQ. How could it be completed by blk_poll()? > + mq = queue_is_mq(q); > + if (!blk_queue_poll(q) || (!mq && !blk_get_bio_poll_ctx())) > bio->bi_opf &= ~REQ_HIPRI; If the use cases are mixed, saying one kernel context may submit IO with and without REQ_TAG at the meantime (though I don't know if this situation exists), then the above code may not work as we expect. For example, dm-XXX will return DM_MAPIO_SUBMITTED and actually submits the cloned bio (with REQ_TAG) with internal kernel threads. Besides, dm-XXX will also allocate bio (without REQ_TAG) of itself for metadata logging or something. When submitting bios (without REQ_TAG), per-task io poll context will be allocated. Later when submitting cloned bios (with REQ_TAG), the poll context already exists and thus REQ_HIPRI is kept for these bios and they are submitted to polling hw queues. > + else if (!mq) > + bio->bi_opf |= REQ_TAG; > } > > static noinline_for_stack bool submit_bio_checks(struct bio *bio) > @@ -893,9 +912,15 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio) > > /* > * Created per-task io poll queue if we supports bio polling > - * and it is one HIPRI bio. > + * and it is one HIPRI bio, and this HIPRI bio has to be from > + * FS. If REQ_TAG isn't set for HIPRI bio, we think it originated > + * from FS. > + * > + * Driver may allocated bio by itself and REQ_TAG is set, but they > + * won't be marked as HIPRI. > */ > blk_create_io_context(q, blk_queue_support_bio_poll(q) && > + !(bio->bi_opf & REQ_TAG) && > (bio->bi_opf & REQ_HIPRI)); > > blk_bio_poll_preprocess(q, bio); > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h > index db026b6ec15a..a1bcade4bcc3 100644 > --- a/include/linux/blk_types.h > +++ b/include/linux/blk_types.h > @@ -394,6 +394,9 @@ enum req_flag_bits { > > __REQ_HIPRI, > > + /* for marking IOs originated from same FS bio in same context */ > + __REQ_TAG, > + > /* for driver use */ > __REQ_DRV, > __REQ_SWAP, /* swapping request. */ > @@ -418,6 +421,7 @@ enum req_flag_bits { > > #define REQ_NOUNMAP (1ULL << __REQ_NOUNMAP) > #define REQ_HIPRI (1ULL << __REQ_HIPRI) > +#define REQ_TAG (1ULL << __REQ_TAG) > > #define REQ_DRV (1ULL << __REQ_DRV) > #define REQ_SWAP (1ULL << __REQ_SWAP) > -- Thanks, Jeffle