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=-0.8 required=3.0 tests=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 3C095C43215 for ; Wed, 20 Nov 2019 17:00:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0FF292071F for ; Wed, 20 Nov 2019 17:00:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="i34jz1Xd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729751AbfKTRAd (ORCPT ); Wed, 20 Nov 2019 12:00:33 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:31655 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728134AbfKTRAd (ORCPT ); Wed, 20 Nov 2019 12:00:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574269232; 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=Cvz2Q4GLLXCvvkELyY3QsZNPG74+YhN9vdrAtOQhB4U=; b=i34jz1Xd3CR8Vg090WW5OBigH17+9bGSbYcTSyaDlMy1Fe7ZdSKkkixfutIGQujFKhpVoU FXS6LmUgqaVzs+wro/XYDe0qGHVeTiJgqDmENfmOhG881pm1pdqEPgTAQREl8alzOzdtba Mc3loqrU6I8NHk+/thtWWLdUtQP+opw= 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-423-2gSBOrfBPlqSRPsWeRUiDw-1; Wed, 20 Nov 2019 12:00:28 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 267D980269C; Wed, 20 Nov 2019 17:00:26 +0000 (UTC) Received: from emilne (unknown [10.18.25.205]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5110D19EE8; Wed, 20 Nov 2019 17:00:20 +0000 (UTC) Message-ID: <9bbcbbb42b659c323c9e0d74aa9b062a3f517d1f.camel@redhat.com> Subject: Re: [PATCH 4/4] scsi: core: don't limit per-LUN queue depth for SSD From: "Ewan D. Milne" To: Hannes Reinecke , Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, "James E . J . Bottomley" , "Martin K . Petersen" , linux-scsi@vger.kernel.org, Sathya Prakash , Chaitra P B , Suganath Prabu Subramani , Kashyap Desai , Sumit Saxena , Shivasharan S , Christoph Hellwig , Bart Van Assche Date: Wed, 20 Nov 2019 12:00:19 -0500 In-Reply-To: <1081145f-3e17-9bc1-2332-50a4b5621ef7@suse.de> References: <20191118103117.978-1-ming.lei@redhat.com> <20191118103117.978-5-ming.lei@redhat.com> <1081145f-3e17-9bc1-2332-50a4b5621ef7@suse.de> Mime-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: 2gSBOrfBPlqSRPsWeRUiDw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 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 Wed, 2019-11-20 at 11:05 +0100, Hannes Reinecke wrote: >=20 > Hmm. >=20 > I must admit I patently don't like this explicit dependency on > blk_nonrot(). Having a conditional counter is just an open invitation to > getting things wrong... >=20 This concerns me as well, it seems like the SCSI ML should have it's own per-device attribute if we actually need to control this per-device instead of on a per-host or per-driver basis. And it seems like this is something that is specific to high-performance drivers, so changing the way this works for all drivers seems a bit much. Ordinarily I'd prefer a host template attribute as Sumanesh proposed, but I dislike wrapping the examination of that and the queue flag in a macro that makes it not obvious how the behavior is affected. (Plus Hannes just submitted submitted the patches to remove .use_cmd_list, which was another piece of ML functionality used by only a few drivers.) Ming's patch does freeze the queue if NONROT is changed by sysfs, but the flag can be changed by other kernel code, e.g. sd_revalidate_disk() clears it and then calls sd_read_block_characteristics() which may set it again. So it's not clear to me how reliable this is. -Ewan