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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 182AFC352A3 for ; Tue, 11 Feb 2020 12:28:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E107E20842 for ; Tue, 11 Feb 2020 12:28:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Jj+QRujA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728772AbgBKM2y (ORCPT ); Tue, 11 Feb 2020 07:28:54 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:21760 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728399AbgBKM2y (ORCPT ); Tue, 11 Feb 2020 07:28:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581424133; 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=uHEOjUhMWrW6Y0OTSi8s083JPpT8Ksjs/CTyJdEAW5w=; b=Jj+QRujAGUd0JbYvMneQn2NyGzoSTXitnUk1JHIi/OIRNkOx3SRiiKp7mCkG+n3nSHvZ48 AoW8hJRLGz734/20KTPmdG31TIzquJy/W18TIl8lihQfo0KiH9n4tHVWzU5r1UOd6cYa98 DzGEbK76XHt4otHHQkFl8LVywwoLAuk= 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-11-tbZMTi2APfmrcMiAbIN50A-1; Tue, 11 Feb 2020 07:28:48 -0500 X-MC-Unique: tbZMTi2APfmrcMiAbIN50A-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F1557800D5E; Tue, 11 Feb 2020 12:28:46 +0000 (UTC) Received: from ming.t460p (ovpn-8-17.pek2.redhat.com [10.72.8.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 10B0B5C120; Tue, 11 Feb 2020 12:28:32 +0000 (UTC) Date: Tue, 11 Feb 2020 20:28:21 +0800 From: Ming Lei To: Tim Walker Cc: linux-block@vger.kernel.org, linux-scsi , linux-nvme@lists.infradead.org Subject: Re: [LSF/MM/BPF TOPIC] NVMe HDD Message-ID: <20200211122821.GA29811@ming.t460p> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Content-Transfer-Encoding: quoted-printable Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Feb 10, 2020 at 02:20:10PM -0500, Tim Walker wrote: > Background: >=20 > NVMe specification has hardened over the decade and now NVMe devices > are well integrated into our customers=E2=80=99 systems. As we look for= ward, > moving HDDs to the NVMe command set eliminates the SAS IOC and driver > stack, consolidating on a single access method for rotational and > static storage technologies. PCIe-NVMe offers near-SATA interface > costs, features and performance suitable for high-cap HDDs, and > optimal interoperability for storage automation, tiering, and > management. We will share some early conceptual results and proposed > salient design goals and challenges surrounding an NVMe HDD. HDD. performance is very sensitive to IO order. Could you provide some background info about NVMe HDD? Such as: - number of hw queues - hw queue depth - will NVMe sort/merge IO among all SQs or not? >=20 >=20 > Discussion Proposal: >=20 > We=E2=80=99d like to share our views and solicit input on: >=20 > -What Linux storage stack assumptions do we need to be aware of as we > develop these devices with drastically different performance > characteristics than traditional NAND? For example, what schedular or > device driver level changes will be needed to integrate NVMe HDDs? IO merge is often important for HDD. IO merge is usually triggered when .queue_rq() returns STS_RESOURCE, so far this condition won't be triggered for NVMe SSD. Also blk-mq kills BDI queue congestion and ioc batching, and causes writeback performance regression[1][2]. What I am thinking is that if we need to switch to use independent IO path for handling SSD and HDD. IO, given the two mediums are so different from performance viewpoint. [1] https://lore.kernel.org/linux-scsi/Pine.LNX.4.44L0.1909181213141.1507= -100000@iolanthe.rowland.org/ [2] https://lore.kernel.org/linux-scsi/20191226083706.GA17974@ming.t460p/ Thanks,=20 Ming