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=-0.9 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 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 00C81C3A5A9 for ; Sat, 2 May 2020 14:29:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA2BE21974 for ; Sat, 2 May 2020 14:29:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fyrZFcjm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728117AbgEBO3h (ORCPT ); Sat, 2 May 2020 10:29:37 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:58902 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728020AbgEBO3h (ORCPT ); Sat, 2 May 2020 10:29:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588429775; 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: in-reply-to:in-reply-to:references:references; bh=b7WJ+MKLLyGXB/QGxxlXuCezmOY5h7z9Abvr4yfXTSs=; b=fyrZFcjmgUNv+faY/6Gy1o2sflLuOLgu3Tq216J/3N8GUwxSbb3w89p6bBzxV+3NS6/SFw GE2gAKOMpnuUvSTepNqLXDtb0W2129mOwkphu+7ont9ytOotaBunj0E7gc+t2ACrt4Mhas VPnbXpyfPXRCk0PXjQ9JTPs14itva0A= 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-379-utRsQoBbOIGMQgDq1-VJTw-1; Sat, 02 May 2020 10:29:31 -0400 X-MC-Unique: utRsQoBbOIGMQgDq1-VJTw-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 0D6301052508; Sat, 2 May 2020 14:29:30 +0000 (UTC) Received: from T590 (ovpn-8-21.pek2.redhat.com [10.72.8.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 98A905D70C; Sat, 2 May 2020 14:29:12 +0000 (UTC) Date: Sat, 2 May 2020 22:29:07 +0800 From: Ming Lei To: Hannes Reinecke Cc: Christoph Hellwig , "Martin K. Petersen" , James Bottomley , John Garry , Bart van Assche , linux-scsi@vger.kernel.org, Hannes Reinecke Subject: Re: [PATCH RFC v3 04/41] csiostor: use reserved command for LUN reset Message-ID: <20200502142907.GE1013372@T590> References: <20200430131904.5847-1-hare@suse.de> <20200430131904.5847-5-hare@suse.de> <20200430151546.GB1005453@T590> <20200501150129.GB1012188@T590> <20200501174505.GC23795@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On Sat, May 02, 2020 at 10:49:32AM +0200, Hannes Reinecke wrote: > On 5/1/20 7:45 PM, Christoph Hellwig wrote: > > On Fri, May 01, 2020 at 11:01:29PM +0800, Ming Lei wrote: > > > > We cannot increase MAX_QUEUE arbitrarily as this is a compile time variable, > > > > which seems to relate to a hardware setting. > > > > > > > > But I can see to update the reserved command functionality for allowing to > > > > fetch commands from the normal I/O tag pool; in the case of LUN reset it > > > > shouldn't make much of a difference as the all I/O is quiesced anyway. > > > > > > It isn't related with reset. > > > > > > This patch reduces active IO queue depth by 1 anytime no matter there is reset > > > or not, and this way may cause performance regression. > > > > But isn't it the right thing to do? How else do we guarantee that > > there always is a tag available for the LU reset? > > > Precisely. One could argue that this is an issue with the current driver, > too; if all tags have timed-out there is no way how we can send a LUN reset > even now. Hence we need to reserve a tag for us to reliably send a LUN > reset. > And this was precisely the problem what sparked off this entire patchset; > some drivers require a valid tag to send internal, non SCSI commands to the > hardware. Could you explain a bit how you conclude that csio_scsi reset hander has to use one unique tag? At least we don't allocate request from block layer for ioctl(SG_SCSI_RESET), see scsi_ioctl_reset(). Also this patch doesn't use the reserved rq->tag too. > And with the current design it requires some really ugly hacks to make this > to work. You also don't explain how csio_eh_lun_reset_handler() is broken and where the ugly hack is in csio scsi too, and how this patch fixes the issue, could you document the exact reason in the commit log? Thanks, Ming