From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Evers Subject: Re: [PATCH 0/2] Change type-2 dif to use rq embedded 32 byte cdb Date: Tue, 27 Nov 2012 11:12:17 -0500 Message-ID: <50B4E661.6020002@redhat.com> References: <1353528468-5664-1-git-send-email-revers@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:61322 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755399Ab2K0QMz (ORCPT ); Tue, 27 Nov 2012 11:12:55 -0500 In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: "Martin K. Petersen" Cc: linux-scsi@vger.kernel.org, chad.dupuis@qlogic.com, giridhar.malavali@qlogic.com, scameron@beardog.cce.hp.com, mike.miller@hp.com, fushun@marvell.com On 11/26/2012 06:58 PM, Martin K. Petersen wrote: >>>>>> "Rob" == Rob Evers writes: > Rob> These patches replace the original t10 type 2 dif mempool > Rob> implementation by increasing the block and scsi cdb maximum sizes > Rob> from 16 to 32 bytes. The cdb embedded in the request structure can > Rob> then be used for type 2 dif commands, or other 32 byte cdbs as > Rob> required. > > Rob> Motivation for this is that type-2 dif commands should be treated > Rob> as any other read/writes generally, without any performance > Rob> penalty. > > We did the mempool because we did not want to penalize everybody else by > always allocating 32-byte CDBs. Type 2 is a really rare corner case. I didn't see a penalty in the non dif case, in the sanity checking I did. If someone has results that indicate otherwise, please indicate. > So while I agree we should handle the UA scenario correctly, I'm not > sure I agree with the fix. Why are you messing with Type 2 devices in > the first place? These should really only be used inside disk arrays. > The previous fix for the mempool race condition was found when one of our partners reported a problem in a system that had type 2 dif storage attached to the host. Use of BLK_MAX_CDB and MAX_COMMAND_SIZE could use some feedback.