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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 60CDDC04FF3 for ; Mon, 24 May 2021 15:01:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D3F861209 for ; Mon, 24 May 2021 15:01:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233499AbhEXPC7 (ORCPT ); Mon, 24 May 2021 11:02:59 -0400 Received: from verein.lst.de ([213.95.11.211]:54895 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233846AbhEXPA6 (ORCPT ); Mon, 24 May 2021 11:00:58 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 5699267373; Mon, 24 May 2021 16:59:28 +0200 (CEST) Date: Mon, 24 May 2021 16:59:28 +0200 From: Christoph Hellwig To: Stefan Hajnoczi Cc: virtualization@lists.linux-foundation.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Jason Wang , Paolo Bonzini , Jens Axboe , slp@redhat.com, sgarzare@redhat.com, "Michael S. Tsirkin" Subject: Re: [PATCH 3/3] virtio_blk: implement blk_mq_ops->poll() Message-ID: <20210524145928.GA3873@lst.de> References: <20210520141305.355961-1-stefanha@redhat.com> <20210520141305.355961-4-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210520141305.355961-4-stefanha@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, May 20, 2021 at 03:13:05PM +0100, Stefan Hajnoczi wrote: > Possible drawbacks of this approach: > > - Hardware virtio_blk implementations may find virtqueue_disable_cb() > expensive since it requires DMA. If such devices become popular then > the virtio_blk driver could use a similar approach to NVMe when > VIRTIO_F_ACCESS_PLATFORM is detected in the future. > > - If a blk_poll() thread is descheduled it not only hurts polling > performance but also delays completion of non-REQ_HIPRI requests on > that virtqueue since vq notifications are disabled. Yes, I think this is a dangerous configuration. What argument exists again just using dedicated poll queues? 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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 0014BC04FF3 for ; Mon, 24 May 2021 14:59:35 +0000 (UTC) Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (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 7023F613B0 for ; Mon, 24 May 2021 14:59:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7023F613B0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=virtualization-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 39A42402E3; Mon, 24 May 2021 14:59:35 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id NsyoCJe7nYYW; Mon, 24 May 2021 14:59:34 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp4.osuosl.org (Postfix) with ESMTP id 98A1240336; Mon, 24 May 2021 14:59:33 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 6DE96C000D; Mon, 24 May 2021 14:59:33 +0000 (UTC) Received: from smtp1.osuosl.org (smtp1.osuosl.org [IPv6:2605:bc80:3010::138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 165FCC0001 for ; Mon, 24 May 2021 14:59:32 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp1.osuosl.org (Postfix) with ESMTP id EA79B82B61 for ; Mon, 24 May 2021 14:59:31 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp1.osuosl.org ([127.0.0.1]) by localhost (smtp1.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id EfEl4JCI0TGC for ; Mon, 24 May 2021 14:59:31 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.8.0 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by smtp1.osuosl.org (Postfix) with ESMTPS id 658CD82B49 for ; Mon, 24 May 2021 14:59:31 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 5699267373; Mon, 24 May 2021 16:59:28 +0200 (CEST) Date: Mon, 24 May 2021 16:59:28 +0200 From: Christoph Hellwig To: Stefan Hajnoczi Subject: Re: [PATCH 3/3] virtio_blk: implement blk_mq_ops->poll() Message-ID: <20210524145928.GA3873@lst.de> References: <20210520141305.355961-1-stefanha@redhat.com> <20210520141305.355961-4-stefanha@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210520141305.355961-4-stefanha@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Jens Axboe , "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-block@vger.kernel.org, Paolo Bonzini , Christoph Hellwig X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Thu, May 20, 2021 at 03:13:05PM +0100, Stefan Hajnoczi wrote: > Possible drawbacks of this approach: > > - Hardware virtio_blk implementations may find virtqueue_disable_cb() > expensive since it requires DMA. If such devices become popular then > the virtio_blk driver could use a similar approach to NVMe when > VIRTIO_F_ACCESS_PLATFORM is detected in the future. > > - If a blk_poll() thread is descheduled it not only hurts polling > performance but also delays completion of non-REQ_HIPRI requests on > that virtqueue since vq notifications are disabled. Yes, I think this is a dangerous configuration. What argument exists again just using dedicated poll queues? _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization