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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78C44C77B7C for ; Fri, 12 May 2023 15:35:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231364AbjELPf5 (ORCPT ); Fri, 12 May 2023 11:35:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53982 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233395AbjELPf4 (ORCPT ); Fri, 12 May 2023 11:35:56 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ECC74198 for ; Fri, 12 May 2023 08:35:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683905711; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ET7hnyRcbg5iW7a6uNqoUY1vArw9P1EwPaP7kXV9CtM=; b=Vr/AiQCCRxUs0UQ/sRTtwPaA0i344UQkl5T8IuC3J2JZ33YO/dv7Zlfai6S9jqoj0m6a6Q 8vnLFWxVYsanPCLJuLhsWGhte+OsZ6LOz6JBsYYC98w+ozrItHVTw5Ac81nV+HDHcZEvB7 GWqxdkYAOHVA5eqIM6phBKinAZzQ8Tw= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-25-JTEOYHAsMteuV8z8oY3_KQ-1; Fri, 12 May 2023 11:35:08 -0400 X-MC-Unique: JTEOYHAsMteuV8z8oY3_KQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E46783813F3F; Fri, 12 May 2023 15:35:07 +0000 (UTC) Received: from ovpn-8-16.pek2.redhat.com (ovpn-8-16.pek2.redhat.com [10.72.8.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 54E28C15BA0; Fri, 12 May 2023 15:35:03 +0000 (UTC) Date: Fri, 12 May 2023 23:34:59 +0800 From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org, Guangwu Zhang , Yu Kuai , ming.lei@redhat.com Subject: Re: [PATCH] blk-mq: don't queue passthrough request into scheduler Message-ID: References: <20230512150328.192908-1-ming.lei@redhat.com> <70478f95-2852-9bf1-f8f7-630c74641c0f@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, May 12, 2023 at 09:25:18AM -0600, Jens Axboe wrote: > On 5/12/23 9:19 AM, Ming Lei wrote: > > On Fri, May 12, 2023 at 09:08:54AM -0600, Jens Axboe wrote: > >> On 5/12/23 9:03?AM, Ming Lei wrote: > >>> Passthrough(pt) request shouldn't be queued to scheduler, especially some > >>> schedulers(such as bfq) supposes that req->bio is always available and > >>> blk-cgroup can be retrieved via bio. > >>> > >>> Sometimes pt request could be part of error handling, so it is better to always > >>> queue it into hctx->dispatch directly. > >>> > >>> Fix this issue by queuing pt request from plug list to hctx->dispatch > >>> directly. > >> > >> Why not just add the check to the BFQ insertion? That would be a lot > >> more trivial and would not be poluting the core with this stuff. > > > > pt request is supposed to be issued to device directly, and we never > > queue it to scheduler before 1c2d2fff6dc0 ("block: wire-up support for > > passthrough plugging"). > > > > some pt request might be part of error handling, and adding it to > > scheduler could cause io hang. > > I'm not suggesting adding it to the scheduler, just having the bypass > "add to dispatch" in a different spot. Originally it is added to dispatch in blk_execute_rq_nowait() for each request, but now we support plug for pt request, that is why I add the bypass in blk_mq_dispatch_plug_list(), and just grab lock for each batch given now blk_execute_rq_nowait() is fast path for nvme uring pt io feature. > > Let me take a look at it... Do we have a reproducer for this issue? Guang Wu and Yu Kuai should have, and I didn't succeed in reproducing it by setting bfq & io.bfq.weight cgroup in my test VM. Thanks, Ming