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,UNPARSEABLE_RELAY 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 CC530C2BA2B for ; Mon, 13 Apr 2020 23:00:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F22F20739 for ; Mon, 13 Apr 2020 23:00:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="wMVfsKne" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389816AbgDMXAD (ORCPT ); Mon, 13 Apr 2020 19:00:03 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:57552 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728050AbgDMXAA (ORCPT ); Mon, 13 Apr 2020 19:00:00 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 03DMmbHX186888; Mon, 13 Apr 2020 22:59:55 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=to : cc : subject : from : references : date : in-reply-to : message-id : mime-version : content-type; s=corp-2020-01-29; bh=DW0a2ib7coI9d+ysr13ixCmPaadlmvTxaylaCDc7ezg=; b=wMVfsKnewosVmTOB0ZFdjlZ229pe6QpBiRCe1w50Z0vb1SfBCPXSyxHJ/OxMJnEG04yX i8MzzHDfPTeAIQlyiaDHuZMuTICE4Td+p+Y5fPdLm8MhIYttt4zYepxbPZkmEGIktRnr ZORriOgSVxKF5XWdNLP5wqs697gxAXcFTWCC93MI7h+LvH4ejnsnjD7iwZA/J9T7EEJ5 t0qb8cQECnigT5gb0S3Uft+6wEiytpyzXUaqGO1kkX4FypNdSeIyseBfeZeSdAOXBooP 6u42wIrt5JA48kebyv8dwAnkBD4agovHhMamoPXJ0/eR1LP+rq5Mi61eacrOI29214e/ lA== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by userp2130.oracle.com with ESMTP id 30b5ar1a3k-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 13 Apr 2020 22:59:55 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 03DMh4uH188683; Mon, 13 Apr 2020 22:57:54 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 30cta8amb7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 13 Apr 2020 22:57:54 +0000 Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 03DMvrUx020829; Mon, 13 Apr 2020 22:57:53 GMT Received: from ca-mkp.ca.oracle.com (/10.159.214.123) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 13 Apr 2020 15:57:53 -0700 To: Douglas Gilbert Cc: linux-scsi@vger.kernel.org, martin.petersen@oracle.com, jejb@linux.vnet.ibm.com, hare@suse.de, Damien.LeMoal@wdc.com Subject: Re: [PATCH v4 06/14] scsi_debug: implement pre-fetch commands From: "Martin K. Petersen" Organization: Oracle Corporation References: <20200225062351.21267-1-dgilbert@interlog.com> <20200225062351.21267-7-dgilbert@interlog.com> Date: Mon, 13 Apr 2020 18:57:51 -0400 In-Reply-To: <20200225062351.21267-7-dgilbert@interlog.com> (Douglas Gilbert's message of "Tue, 25 Feb 2020 01:23:43 -0500") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1.92 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9590 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 suspectscore=0 spamscore=0 adultscore=0 mlxscore=0 phishscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004130165 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9590 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 impostorscore=0 clxscore=1015 priorityscore=1501 malwarescore=0 phishscore=0 spamscore=0 mlxlogscore=999 suspectscore=0 adultscore=0 mlxscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004130165 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org Doug, > Many disks implement the SCSI PRE-FETCH commands. One use case might > be a disk-to-disk compare, say between disks A and B. Then this > sequence of commands might be used: PRE-FETCH(from B, IMMED), > READ(from A), VERIFY (BYTCHK=1 on B with data returned from READ). The > PRE-FETCH (which returns quickly due to the IMMED) fetches the data > from the media into B's cache which should speed the trailing VERIFY > command. The next chunk of the compare might be done in parallel, > with A and B reversed. Minor nit: I agree with the code and the use case. But the commit description should reflect what the code actually does (not much in the absence of cache, etc.) -- Martin K. Petersen Oracle Linux Engineering