From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: [PATCH 1/3] sd: don't bother spinning up disks on resume Date: Sun, 17 Nov 2013 18:54:34 -0500 Message-ID: <5289573A.9070307@interlog.com> References: <527AF287.7020700@ubuntu.com> <927e15641f27b46f206f8ae8110201c8fd77b7e1.1383789225.git.psusi@ubuntu.com> <527BDA11.6060603@interlog.com> <527C0349.5010301@ubuntu.com> <1384626031.3614.7.camel@dabdike.int.hansenpartnership.com> <52883CE9.9040102@ubuntu.com> <1384670620.3614.24.camel@dabdike.int.hansenpartnership.com> <5288EBA6.3070609@ubuntu.com> Reply-To: dgilbert@interlog.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from smtp.infotech.no ([82.134.31.41]:54179 "EHLO smtp.infotech.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751267Ab3KQXy7 (ORCPT ); Sun, 17 Nov 2013 18:54:59 -0500 In-Reply-To: <5288EBA6.3070609@ubuntu.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Phillip Susi , James Bottomley Cc: todd.e.brandt@linux.intel.com, linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org, tj@kernel.org On 13-11-17 11:15 AM, Phillip Susi wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA512 > > On 11/17/2013 01:43 AM, James Bottomley wrote: >> OK, so three people have now told you that's not how the code >> works. Why don't you just read it? because there's not really much >> point us reading your patches until you do. > > I have, which is why I said it handles it via scsi_eh_stu. If I'm not > understanding it correctly, then by all means, explain. Even if the SCSI EH code does spin-up the disk, it is inefficient and undesirable to send a device into EH for what is a normal, predictable situation (i.e. that a SCSI disk will need a START STOP UNIT (start) command as part of a resume operation). A big server machine could have thousands of SCSI disks (many potentially virtual). Sending them all into EH during a resume would be a really good test for EH, but horrible for performance. If I was designing the SCSI EH I would probably assume not all disks would go into EH at roughly the same time. Also if that many devices went into EH on the same controller (HBA) it might be reasonable to assume that the controller they share needs resetting. Doug Gilbert