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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 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 DD493C433B4 for ; Fri, 16 Apr 2021 10:20:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ACDF36115B for ; Fri, 16 Apr 2021 10:20:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235192AbhDPKUs (ORCPT ); Fri, 16 Apr 2021 06:20:48 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:46971 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235167AbhDPKUs (ORCPT ); Fri, 16 Apr 2021 06:20:48 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0UVk99mh_1618568422; Received: from admindeMacBook-Pro-2.local(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0UVk99mh_1618568422) by smtp.aliyun-inc.com(127.0.0.1); Fri, 16 Apr 2021 18:20:22 +0800 Subject: Re: [PATCH] block: introduce QUEUE_FLAG_POLL_CAP flag To: Ming Lei Cc: snitzer@redhat.com, axboe@kernel.dk, linux-block@vger.kernel.org, dm-devel@redhat.com References: <20210401021927.343727-12-ming.lei@redhat.com> <20210416080037.26335-1-jefflexu@linux.alibaba.com> From: JeffleXu Message-ID: Date: Fri, 16 Apr 2021 18:20:22 +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: 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 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. Yes it is. > > So why not start with the simplest approach(always capable of polling) > which does meet normal bio based polling requirement? > I agree if we have no better way. Though the handling of "sysfs/io_poll" is somehow inconsistent between blk-mq and bio-based device then. -- Thanks, Jeffle