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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 CCF2FC43461 for ; Thu, 15 Apr 2021 13:09:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AD811611F1 for ; Thu, 15 Apr 2021 13:09:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233037AbhDONJr (ORCPT ); Thu, 15 Apr 2021 09:09:47 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:50455 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233213AbhDONJf (ORCPT ); Thu, 15 Apr 2021 09:09:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618492151; 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=4BSGNPrb+Ur/0ielLLQl6KwM595K6/ayB7X/f5fp3gA=; b=WRNj997N7v0M/RkwCtu5HeV8O2vdhlv6xOMMNyBPQDGD6IB12vMf56lNBRHJUNdJ/BFdCR hXl9boqWo7E/VMmRT9BqDm53Vu2K2gw+tDEYGq58DE1tm7NndVMlEbbMFlUzli+k++9Y85 qgO2qy8QpzA24M+CMSkT+eAoXcUhAws= 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-500-Hqy-LLzXP9WNsB_Z4XFd3A-1; Thu, 15 Apr 2021 09:09:10 -0400 X-MC-Unique: Hqy-LLzXP9WNsB_Z4XFd3A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E415A801814; Thu, 15 Apr 2021 13:09:08 +0000 (UTC) Received: from T590 (ovpn-12-95.pek2.redhat.com [10.72.12.95]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6A68F16D36; Thu, 15 Apr 2021 13:08:56 +0000 (UTC) Date: Thu, 15 Apr 2021 21:08:52 +0800 From: Ming Lei To: JeffleXu Cc: Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org, Mike Snitzer , dm-devel@redhat.com, Hannes Reinecke Subject: Re: [PATCH V5 11/12] block: add poll_capable method to support bio-based IO polling Message-ID: References: <20210401021927.343727-1-ming.lei@redhat.com> <20210401021927.343727-12-ming.lei@redhat.com> <20210412093856.GA978201@infradead.org> <5f30059d-6650-8268-b681-d8567ac1c509@linux.alibaba.com> <0ceb3060-bce4-c39d-26cf-8c715ebbfd51@linux.alibaba.com> <5f2542e4-1c36-71e8-5c72-a85b23c98b72@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5f2542e4-1c36-71e8-5c72-a85b23c98b72@linux.alibaba.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Apr 15, 2021 at 07:21:52PM +0800, JeffleXu wrote: > > > On 4/15/21 6:06 PM, Ming Lei wrote: > > On Thu, Apr 15, 2021 at 05:21:56PM +0800, JeffleXu wrote: > >> > >> > >> On 4/15/21 3:43 PM, Ming Lei wrote: > >>> On Thu, Apr 15, 2021 at 09:34:36AM +0800, JeffleXu wrote: > >>>> > >>>> > >>>> On 4/14/21 7:24 PM, Ming Lei wrote: > >>>>> On Wed, Apr 14, 2021 at 04:38:25PM +0800, JeffleXu wrote: > >>>>>> > >>>>>> > >>>>>> On 4/12/21 5:38 PM, Christoph Hellwig wrote: > >>>>>>> On Thu, Apr 01, 2021 at 10:19:26AM +0800, Ming Lei wrote: > >>>>>>>> From: Jeffle Xu > >>>>>>>> > >>>>>>>> This method can be used to check if bio-based device supports IO polling > >>>>>>>> or not. For mq devices, checking for hw queue in polling mode is > >>>>>>>> adequate, while the sanity check shall be implementation specific for > >>>>>>>> bio-based devices. For example, dm device needs to check if all > >>>>>>>> underlying devices are capable of IO polling. > >>>>>>>> > >>>>>>>> Though bio-based device may have done the sanity check during the > >>>>>>>> device initialization phase, cacheing the result of this sanity check > >>>>>>>> (such as by cacheing in the queue_flags) may not work. Because for dm > >>>>>>>> devices, users could change the state of the underlying devices through > >>>>>>>> '/sys/block//io_poll', bypassing the dm device above. In this case, > >>>>>>>> the cached result of the very beginning sanity check could be > >>>>>>>> out-of-date. Thus the sanity check needs to be done every time 'io_poll' > >>>>>>>> is to be modified. > >>>>>>> > >>>>>>> I really don't think thi should be a method, and I really do dislike > >>>>>>> how we have all this "if (is_mq)" junk. Why can't we have a flag on > >>>>>>> the gendisk that signals if the device can support polling that > >>>>>>> is autoamtically set for blk-mq and as-needed by bio based drivers? > >>>>>> > >>>>>> That would consume one more bit of queue->queue_flags. > >>>>>> > >>>>>> Besides, DM/MD is somehow special here that when one of the underlying > >>>>>> devices is disabled polling through '/sys/block//io_poll', > >>>>>> currently there's no mechanism notifying the above MD/DM to clear the > >>>>>> previously set queue_flags. Thus the outdated queue_flags still > >>>>>> indicates this DM/MD is capable of polling, while in fact one of the > >>>>>> underlying device has been disabled for polling. > >>>>> > >>>>> Right, just like there isn't queue limit progagation. > >>>>> > >>>>> Another blocker could be that bio based queue doesn't support queue > >>>>> freezing. > >>>> > >>>> Do you mean the queue freezing is called in the following code snippet? > >>>> > >>>> ``` > >>>> static ssize_t queue_poll_store(struct request_queue *q, const char > >>>> *page, size_t count) > >>>> { > >>>> ... > >>>> if (poll_on) { > >>>> blk_queue_flag_set(QUEUE_FLAG_POLL, q); > >>>> } else { > >>>> blk_mq_freeze_queue(q); > >>>> blk_queue_flag_clear(QUEUE_FLAG_POLL, q); > >>>> blk_mq_unfreeze_queue(q); > >>>> } > >>>> ``` > >>> > >>> Yes, if it is a bio based queue. Or bio queued queue(DM, MD or others) may > >>> use freeze_queue to do similar thing. > >>> > >>>> > >>>> And I can't understand how bio-based queue doesn't support queue freezing. > >>>> > >>>> ``` > >>>> submit_bio_noacct > >>>> __submit_bio_noacct > >>>> bio_queue_enter > >>>> ``` > >>>> > >>>> Every time submitting a bio, bio_queue_enter() will be called, and once > >>>> the queue has been frozen, bio_queue_enter() will wait there until the > >>>> queue is unfrozen. > >>> > >>> Not like blk-mq, the refcount is just grabbed during submission for bio based > >>> queue. > >> > >> Could you please explain it more detailed .... > > > > Please see __submit_bio(), in which the queue ref is dropped. > > > >> > >> > >> I will research a bit and see if we can extend freeze queue for > >>> covering bio based queue. One trouble is that bio is ended before > >>> freeing request. > >>> > >>>> > >>>>> > >>>>>> > >>>>>> Mike had ever suggested that we can trust the queue_flag, and clear the > >>>>>> outdated queue_flags when later the IO submission or polling routine > >>>>>> finally finds that the device is not capable of polling. Currently > >>>>>> submit_bio_checks() will silently clear the REQ_HIPRI flag and still > >>>>>> submit the bio when the device is actually not capable of polling. To > >>>>>> fix the issue, could we break the submission and return an error code in > >>>>>> submit_bio_checks() if the device is not capable of polling when > >>>>>> submitting HIPRI bio? > >>>>> > >>>>> I think we may just leave it alone, if underlying queue becomes not pollable, > >>>>> the bio still can be submitted & completed via IRQ, just not efficient enough. > >>>> > >>>> Yes it still works. I agree if there's no better solution... > >>>> > >>>> And what about the issue Christoph originally concerned? Do we use one > >>>> more flag bit indicating if the queue capable of polling, or the > >>>> poll_capable() method way? > >>> > >>> Just wondering why we can't use QUEUE_FLAG_POLL simply? If user wants to > >>> enable it, let's do it for them. And bio driver can start with default poll > >>> state by checking underlying queues. > >>> > >> > >> Consider the following scenario: QUEUE_FLAG_POLL is set after > >> initialization, indicating the device capable of polling; then polling > >> is turned off by '/sys/block//io_poll', thus QUEUE_FLAG_POLL is > >> cleared. > > > > If the flag is cleared, the bio will be submitted to irq queue, what is > > the problem? > > > > The IO path has no problem. It is the control path. If you want to turn Can you explain a bit what the control path is? > on polling then, you have to check if the device capable of polling, > while QUEUE_FLAG_POLL has been cleared in this case. IOW you can't rely > on QUEUE_FLAG_POLL to see if the device has the **ability** of polling. > QUEUE_FLAG_POLL flag only indicates if polling is turned on or off > currently. For bio based driver, I'd suggest to start with do polling simply if QUEUE_FLAG_POLL is set in bio request queue flag. The flag can be enabled/disabled during initialization, or via sysfs. That said we can start with always thinking the bio queue is capable of io polling. 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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 9D3C7C433ED for ; Thu, 15 Apr 2021 13:09:25 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 4BFF0613B0 for ; Thu, 15 Apr 2021 13:09:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4BFF0613B0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; 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Thu, 15 Apr 2021 13:09:17 +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 283A7100E113; Thu, 15 Apr 2021 13:09:15 +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 8D3711806D15; Thu, 15 Apr 2021 13:09:12 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 13FD98Jm016140 for ; Thu, 15 Apr 2021 09:09:08 -0400 Received: by smtp.corp.redhat.com (Postfix) id E1E4E16E4D; Thu, 15 Apr 2021 13:09:08 +0000 (UTC) Received: from T590 (ovpn-12-95.pek2.redhat.com [10.72.12.95]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6A68F16D36; Thu, 15 Apr 2021 13:08:56 +0000 (UTC) Date: Thu, 15 Apr 2021 21:08:52 +0800 From: Ming Lei To: JeffleXu Message-ID: References: <20210401021927.343727-1-ming.lei@redhat.com> <20210401021927.343727-12-ming.lei@redhat.com> <20210412093856.GA978201@infradead.org> <5f30059d-6650-8268-b681-d8567ac1c509@linux.alibaba.com> <0ceb3060-bce4-c39d-26cf-8c715ebbfd51@linux.alibaba.com> <5f2542e4-1c36-71e8-5c72-a85b23c98b72@linux.alibaba.com> MIME-Version: 1.0 In-Reply-To: <5f2542e4-1c36-71e8-5c72-a85b23c98b72@linux.alibaba.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-loop: dm-devel@redhat.com Cc: Jens Axboe , linux-block@vger.kernel.org, Mike Snitzer , Christoph Hellwig , dm-devel@redhat.com Subject: Re: [dm-devel] [PATCH V5 11/12] block: add poll_capable method to support bio-based IO polling 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 2.84 on 10.5.11.22 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 Thu, Apr 15, 2021 at 07:21:52PM +0800, JeffleXu wrote: > > > On 4/15/21 6:06 PM, Ming Lei wrote: > > On Thu, Apr 15, 2021 at 05:21:56PM +0800, JeffleXu wrote: > >> > >> > >> On 4/15/21 3:43 PM, Ming Lei wrote: > >>> On Thu, Apr 15, 2021 at 09:34:36AM +0800, JeffleXu wrote: > >>>> > >>>> > >>>> On 4/14/21 7:24 PM, Ming Lei wrote: > >>>>> On Wed, Apr 14, 2021 at 04:38:25PM +0800, JeffleXu wrote: > >>>>>> > >>>>>> > >>>>>> On 4/12/21 5:38 PM, Christoph Hellwig wrote: > >>>>>>> On Thu, Apr 01, 2021 at 10:19:26AM +0800, Ming Lei wrote: > >>>>>>>> From: Jeffle Xu > >>>>>>>> > >>>>>>>> This method can be used to check if bio-based device supports IO polling > >>>>>>>> or not. For mq devices, checking for hw queue in polling mode is > >>>>>>>> adequate, while the sanity check shall be implementation specific for > >>>>>>>> bio-based devices. For example, dm device needs to check if all > >>>>>>>> underlying devices are capable of IO polling. > >>>>>>>> > >>>>>>>> Though bio-based device may have done the sanity check during the > >>>>>>>> device initialization phase, cacheing the result of this sanity check > >>>>>>>> (such as by cacheing in the queue_flags) may not work. Because for dm > >>>>>>>> devices, users could change the state of the underlying devices through > >>>>>>>> '/sys/block//io_poll', bypassing the dm device above. In this case, > >>>>>>>> the cached result of the very beginning sanity check could be > >>>>>>>> out-of-date. Thus the sanity check needs to be done every time 'io_poll' > >>>>>>>> is to be modified. > >>>>>>> > >>>>>>> I really don't think thi should be a method, and I really do dislike > >>>>>>> how we have all this "if (is_mq)" junk. Why can't we have a flag on > >>>>>>> the gendisk that signals if the device can support polling that > >>>>>>> is autoamtically set for blk-mq and as-needed by bio based drivers? > >>>>>> > >>>>>> That would consume one more bit of queue->queue_flags. > >>>>>> > >>>>>> Besides, DM/MD is somehow special here that when one of the underlying > >>>>>> devices is disabled polling through '/sys/block//io_poll', > >>>>>> currently there's no mechanism notifying the above MD/DM to clear the > >>>>>> previously set queue_flags. Thus the outdated queue_flags still > >>>>>> indicates this DM/MD is capable of polling, while in fact one of the > >>>>>> underlying device has been disabled for polling. > >>>>> > >>>>> Right, just like there isn't queue limit progagation. > >>>>> > >>>>> Another blocker could be that bio based queue doesn't support queue > >>>>> freezing. > >>>> > >>>> Do you mean the queue freezing is called in the following code snippet? > >>>> > >>>> ``` > >>>> static ssize_t queue_poll_store(struct request_queue *q, const char > >>>> *page, size_t count) > >>>> { > >>>> ... > >>>> if (poll_on) { > >>>> blk_queue_flag_set(QUEUE_FLAG_POLL, q); > >>>> } else { > >>>> blk_mq_freeze_queue(q); > >>>> blk_queue_flag_clear(QUEUE_FLAG_POLL, q); > >>>> blk_mq_unfreeze_queue(q); > >>>> } > >>>> ``` > >>> > >>> Yes, if it is a bio based queue. Or bio queued queue(DM, MD or others) may > >>> use freeze_queue to do similar thing. > >>> > >>>> > >>>> And I can't understand how bio-based queue doesn't support queue freezing. > >>>> > >>>> ``` > >>>> submit_bio_noacct > >>>> __submit_bio_noacct > >>>> bio_queue_enter > >>>> ``` > >>>> > >>>> Every time submitting a bio, bio_queue_enter() will be called, and once > >>>> the queue has been frozen, bio_queue_enter() will wait there until the > >>>> queue is unfrozen. > >>> > >>> Not like blk-mq, the refcount is just grabbed during submission for bio based > >>> queue. > >> > >> Could you please explain it more detailed .... > > > > Please see __submit_bio(), in which the queue ref is dropped. > > > >> > >> > >> I will research a bit and see if we can extend freeze queue for > >>> covering bio based queue. One trouble is that bio is ended before > >>> freeing request. > >>> > >>>> > >>>>> > >>>>>> > >>>>>> Mike had ever suggested that we can trust the queue_flag, and clear the > >>>>>> outdated queue_flags when later the IO submission or polling routine > >>>>>> finally finds that the device is not capable of polling. Currently > >>>>>> submit_bio_checks() will silently clear the REQ_HIPRI flag and still > >>>>>> submit the bio when the device is actually not capable of polling. To > >>>>>> fix the issue, could we break the submission and return an error code in > >>>>>> submit_bio_checks() if the device is not capable of polling when > >>>>>> submitting HIPRI bio? > >>>>> > >>>>> I think we may just leave it alone, if underlying queue becomes not pollable, > >>>>> the bio still can be submitted & completed via IRQ, just not efficient enough. > >>>> > >>>> Yes it still works. I agree if there's no better solution... > >>>> > >>>> And what about the issue Christoph originally concerned? Do we use one > >>>> more flag bit indicating if the queue capable of polling, or the > >>>> poll_capable() method way? > >>> > >>> Just wondering why we can't use QUEUE_FLAG_POLL simply? If user wants to > >>> enable it, let's do it for them. And bio driver can start with default poll > >>> state by checking underlying queues. > >>> > >> > >> Consider the following scenario: QUEUE_FLAG_POLL is set after > >> initialization, indicating the device capable of polling; then polling > >> is turned off by '/sys/block//io_poll', thus QUEUE_FLAG_POLL is > >> cleared. > > > > If the flag is cleared, the bio will be submitted to irq queue, what is > > the problem? > > > > The IO path has no problem. It is the control path. If you want to turn Can you explain a bit what the control path is? > on polling then, you have to check if the device capable of polling, > while QUEUE_FLAG_POLL has been cleared in this case. IOW you can't rely > on QUEUE_FLAG_POLL to see if the device has the **ability** of polling. > QUEUE_FLAG_POLL flag only indicates if polling is turned on or off > currently. For bio based driver, I'd suggest to start with do polling simply if QUEUE_FLAG_POLL is set in bio request queue flag. The flag can be enabled/disabled during initialization, or via sysfs. That said we can start with always thinking the bio queue is capable of io polling. Thanks, Ming -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel