From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Smart Subject: Re: [RFC] [Last Rites] fc transport: extensions for fast fail and dev loss Date: Thu, 10 Aug 2006 12:38:51 -0400 Message-ID: <44DB611B.5020001@emulex.com> References: <1150829123.16981.1.camel@localhost.localdomain> <44D8CFD3.9050408@emulex.com> <44D90878.7000903@sgi.com> <44D90CE8.70006@sgi.com> <44D9FFCE.4040702@sgi.com> Reply-To: James.Smart@Emulex.Com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from emulex.emulex.com ([138.239.112.1]:5562 "EHLO emulex.emulex.com") by vger.kernel.org with ESMTP id S1161444AbWHJQi5 (ORCPT ); Thu, 10 Aug 2006 12:38:57 -0400 In-Reply-To: <44D9FFCE.4040702@sgi.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Michael Reed Cc: linux-scsi Michael Reed wrote: > In thinking about this over night, I would like to withdraw my previous > comments. (Hence the snip!) > > Let's take the case of real time capture from a device and > post processing of that data. The capture operation would > likely want a fast fail to avoid dropping data. The post > processing of that data would like to wait for the device > to return to avoid disruption and potential premature termination > of the job. > > Under the above scenario, assuming it's a valid scenario, are there > mechanisms in place to allow an application to tag an i/o stream > for fast fail? Two comments: - This conflicts with Christoph's last comment about fast_fail failing all i/o's. I prefer the fail all, as its the easier, more straight-forward approach. Easiest to explain behavior for too. - As for tagging i/o from an application, the only places I see in the kernel setting the flags that make REQ_FAILFAST get set are strictly in-the-kernel items (multipath). I don't see any way for an application to mark this. It implies that to do what you stated above, requires the app has to serially perform each mode - and to do so at a target level. E.g. set fast fail, perform capture, set no fast fail, perform post processing. -- james s