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=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E6DC9C433B4 for ; Mon, 19 Apr 2021 02:21:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C017C60FF3 for ; Mon, 19 Apr 2021 02:21:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237275AbhDSCWR (ORCPT ); Sun, 18 Apr 2021 22:22:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:47069 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233117AbhDSCWQ (ORCPT ); Sun, 18 Apr 2021 22:22:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618798907; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=VkWRu5hLnZo5fr3qFvYuVX/r+7arjgAsCKIuVdtVwyc=; b=iAu/ZhgHe0cOh8eg5dE/GYvEt+eSGjwyBXaFnZBfXoHx97hD+eYHlOCgZaXQ9xkKzbsvFW +SwYJhLCdDQhmTkVFTw/v7UWZ6do9HRSsEQwRyK1yAUc7FYtlQ9dhJBPWO0Sgx8hISKTjP RpiIvMI1a2Qkq91C/yYsNBRGOezNofk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-361-ikhi7jRLM1yCIaJYQuslQA-1; Sun, 18 Apr 2021 22:21:45 -0400 X-MC-Unique: ikhi7jRLM1yCIaJYQuslQA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4D37D107ACC7; Mon, 19 Apr 2021 02:21:44 +0000 (UTC) Received: from T590 (ovpn-12-222.pek2.redhat.com [10.72.12.222]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 72E50138FB; Mon, 19 Apr 2021 02:21:28 +0000 (UTC) Date: Mon, 19 Apr 2021 10:21:26 +0800 From: Ming Lei To: JeffleXu Cc: snitzer@redhat.com, axboe@kernel.dk, linux-block@vger.kernel.org, dm-devel@redhat.com Subject: Re: [PATCH] block: introduce QUEUE_FLAG_POLL_CAP flag Message-ID: References: <20210401021927.343727-12-ming.lei@redhat.com> <20210416080037.26335-1-jefflexu@linux.alibaba.com> <1fb6e15e-fb4d-a2bf-9f65-2ae2aa15a8a2@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1fb6e15e-fb4d-a2bf-9f65-2ae2aa15a8a2@linux.alibaba.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Sat, Apr 17, 2021 at 10:06:53PM +0800, JeffleXu wrote: > > > On 4/16/21 5:07 PM, Ming Lei wrote: > > On Fri, Apr 16, 2021 at 04:00:37PM +0800, Jeffle Xu wrote: > >> Hi, > >> How about this patch to remove the extra poll_capable() method? > >> > >> And the following 'dm: support IO polling for bio-based dm device' needs > >> following change. > >> > >> ``` > >> + /* > >> + * Check for request-based device is remained to > >> + * dm_mq_init_request_queue()->blk_mq_init_allocated_queue(). > >> + * For bio-based device, only set QUEUE_FLAG_POLL when all underlying > >> + * devices supporting polling. > >> + */ > >> + if (__table_type_bio_based(t->type)) { > >> + if (dm_table_supports_poll(t)) { > >> + blk_queue_flag_set(QUEUE_FLAG_POLL_CAP, q); > >> + blk_queue_flag_set(QUEUE_FLAG_POLL, q); > >> + } > >> + else { > >> + blk_queue_flag_clear(QUEUE_FLAG_POLL, q); > >> + blk_queue_flag_clear(QUEUE_FLAG_POLL_CAP, q); > >> + } > >> + } > >> ``` > > > > Frankly speaking, I don't see any value of using QUEUE_FLAG_POLL_CAP for > > DM, and the result is basically subset of treating DM as always being capable > > of polling. > > > > Also underlying queue change(either limits or flag) won't be propagated > > to DM/MD automatically. Strictly speaking it doesn't matter if all underlying > > queues are capable of supporting polling at the exact time of 'write sysfs/poll', > > cause any of them may change in future. > > > > So why not start with the simplest approach(always capable of polling) > > which does meet normal bio based polling requirement? > > > > I find one scenario where this issue may matter. Consider the scenario > where HIPRI bios are submitted to DM device though **all** underlying > devices has been disabled for polling. In this case, a **valid** cookie > (pid of current submitting process) is still returned. Then if @spin of > the following blk_poll() is true, blk_poll() will get stuck in dead loop > because blk_mq_poll() always returns 0, since previously submitted bios > are all enqueued into IRQ hw queue. > > Maybe you need to re-remove the bio from the poll context if the > returned cookie is BLK_QC_T_NONE? It won't be one issue, see blk_bio_poll_preprocess() which is called from submit_bio_checks(), so any bio's HIPRI will be cleared if the queue doesn't support POLL, that code does cover underlying bios. > > > Something like: > > -static blk_qc_t __submit_bio_noacct(struct bio *bio) > +static blk_qc_t __submit_bio_noacct_ctx(struct bio *bio, struct > io_context *ioc) > { > struct bio_list bio_list_on_stack[2]; > blk_qc_t ret = BLK_QC_T_NONE; > @@ -1047,7 +1163,15 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio) > bio_list_on_stack[1] = bio_list_on_stack[0]; > bio_list_init(&bio_list_on_stack[0]); > > if (ioc && queue_is_mq(q) && (bio->bi_opf & REQ_HIPRI)) { REQ_HIPRI won't be set for underlying bios which queue doesn't support poll, so this branch won't be reached. And the submission queue will be empty, and blk_poll() for DM/MD(bio based queue) checks nothing, but the polling won't be stopped until the iocb is completed. And this handling is actually same with current polling on IRQ based queue. > bool queued = blk_bio_poll_prep_submit(ioc, bio); > > ret = __submit_bio(bio); > + if (queued && !blk_qc_t_valid(ret)) > /* TODO:remove bio from poll_context */ > > bio_set_private_data(bio, ret); > } else { > ret = __submit_bio(bio); > } > > > Then if you'd like fix this in this way, the returned value of > .submit_bio() of DM/MD also needs to return BLK_QC_T_NONE now. Currently > .submit_bio() of DM actually returns the cookie of the last split bio > (to underlying mq deivice). I am a bit confused, this patch requires .submit_bio() of DM/MD(bio based queue) to return either 0 or pid of the submission task. Thanks, Ming 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=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 0F155C433ED for ; Mon, 19 Apr 2021 02:23:03 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 90CFF61073 for ; Mon, 19 Apr 2021 02:23:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 90CFF61073 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=tempfail smtp.mailfrom=dm-devel-bounces@redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618798981; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:list-id:list-help: list-unsubscribe:list-subscribe:list-post; bh=knnn5RYwDhxpEnEdD+TLfMJBmO1Ve6dt0ES1CVqvp4Y=; b=boMof0nGzHjRpbDph64EugKVkzt6l7L9o6aqTMHjbeP7GfUAof3c/hHZpRKDMUdUaxWJ6k ahoiwlhXXY0lXycCJOZIMBA2G6Zo1SxJWsNClJpFC5jgvV5fEG/c4hULV5O9JS/XVFH7Yb TCTx1kDXH6EJObcI/ln1SY7m5f4BddQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-195-Pc2fUXmoP1SsAfUqPIpuNw-1; Sun, 18 Apr 2021 22:22:59 -0400 X-MC-Unique: Pc2fUXmoP1SsAfUqPIpuNw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E3B78501F0; Mon, 19 Apr 2021 02:22:53 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 88CAA610F1; Mon, 19 Apr 2021 02:22:51 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id 357BB1806D17; Mon, 19 Apr 2021 02:22:47 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 13J2Likk024372 for ; Sun, 18 Apr 2021 22:21:44 -0400 Received: by smtp.corp.redhat.com (Postfix) id 4C6DF610F1; Mon, 19 Apr 2021 02:21:44 +0000 (UTC) Received: from T590 (ovpn-12-222.pek2.redhat.com [10.72.12.222]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 72E50138FB; Mon, 19 Apr 2021 02:21:28 +0000 (UTC) Date: Mon, 19 Apr 2021 10:21:26 +0800 From: Ming Lei To: JeffleXu Message-ID: References: <20210401021927.343727-12-ming.lei@redhat.com> <20210416080037.26335-1-jefflexu@linux.alibaba.com> <1fb6e15e-fb4d-a2bf-9f65-2ae2aa15a8a2@linux.alibaba.com> MIME-Version: 1.0 In-Reply-To: <1fb6e15e-fb4d-a2bf-9f65-2ae2aa15a8a2@linux.alibaba.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-loop: dm-devel@redhat.com Cc: axboe@kernel.dk, linux-block@vger.kernel.org, dm-devel@redhat.com, snitzer@redhat.com Subject: Re: [dm-devel] [PATCH] block: introduce QUEUE_FLAG_POLL_CAP flag X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Sat, Apr 17, 2021 at 10:06:53PM +0800, JeffleXu wrote: > > > On 4/16/21 5:07 PM, Ming Lei wrote: > > On Fri, Apr 16, 2021 at 04:00:37PM +0800, Jeffle Xu wrote: > >> Hi, > >> How about this patch to remove the extra poll_capable() method? > >> > >> And the following 'dm: support IO polling for bio-based dm device' needs > >> following change. > >> > >> ``` > >> + /* > >> + * Check for request-based device is remained to > >> + * dm_mq_init_request_queue()->blk_mq_init_allocated_queue(). > >> + * For bio-based device, only set QUEUE_FLAG_POLL when all underlying > >> + * devices supporting polling. > >> + */ > >> + if (__table_type_bio_based(t->type)) { > >> + if (dm_table_supports_poll(t)) { > >> + blk_queue_flag_set(QUEUE_FLAG_POLL_CAP, q); > >> + blk_queue_flag_set(QUEUE_FLAG_POLL, q); > >> + } > >> + else { > >> + blk_queue_flag_clear(QUEUE_FLAG_POLL, q); > >> + blk_queue_flag_clear(QUEUE_FLAG_POLL_CAP, q); > >> + } > >> + } > >> ``` > > > > Frankly speaking, I don't see any value of using QUEUE_FLAG_POLL_CAP for > > DM, and the result is basically subset of treating DM as always being capable > > of polling. > > > > Also underlying queue change(either limits or flag) won't be propagated > > to DM/MD automatically. Strictly speaking it doesn't matter if all underlying > > queues are capable of supporting polling at the exact time of 'write sysfs/poll', > > cause any of them may change in future. > > > > So why not start with the simplest approach(always capable of polling) > > which does meet normal bio based polling requirement? > > > > I find one scenario where this issue may matter. Consider the scenario > where HIPRI bios are submitted to DM device though **all** underlying > devices has been disabled for polling. In this case, a **valid** cookie > (pid of current submitting process) is still returned. Then if @spin of > the following blk_poll() is true, blk_poll() will get stuck in dead loop > because blk_mq_poll() always returns 0, since previously submitted bios > are all enqueued into IRQ hw queue. > > Maybe you need to re-remove the bio from the poll context if the > returned cookie is BLK_QC_T_NONE? It won't be one issue, see blk_bio_poll_preprocess() which is called from submit_bio_checks(), so any bio's HIPRI will be cleared if the queue doesn't support POLL, that code does cover underlying bios. > > > Something like: > > -static blk_qc_t __submit_bio_noacct(struct bio *bio) > +static blk_qc_t __submit_bio_noacct_ctx(struct bio *bio, struct > io_context *ioc) > { > struct bio_list bio_list_on_stack[2]; > blk_qc_t ret = BLK_QC_T_NONE; > @@ -1047,7 +1163,15 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio) > bio_list_on_stack[1] = bio_list_on_stack[0]; > bio_list_init(&bio_list_on_stack[0]); > > if (ioc && queue_is_mq(q) && (bio->bi_opf & REQ_HIPRI)) { REQ_HIPRI won't be set for underlying bios which queue doesn't support poll, so this branch won't be reached. And the submission queue will be empty, and blk_poll() for DM/MD(bio based queue) checks nothing, but the polling won't be stopped until the iocb is completed. And this handling is actually same with current polling on IRQ based queue. > bool queued = blk_bio_poll_prep_submit(ioc, bio); > > ret = __submit_bio(bio); > + if (queued && !blk_qc_t_valid(ret)) > /* TODO:remove bio from poll_context */ > > bio_set_private_data(bio, ret); > } else { > ret = __submit_bio(bio); > } > > > Then if you'd like fix this in this way, the returned value of > .submit_bio() of DM/MD also needs to return BLK_QC_T_NONE now. Currently > .submit_bio() of DM actually returns the cookie of the last split bio > (to underlying mq deivice). I am a bit confused, this patch requires .submit_bio() of DM/MD(bio based queue) to return either 0 or pid of the submission task. Thanks, Ming -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel