From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bartlomiej Zolnierkiewicz Subject: Re: [RFC/PATCH 0/7] enable honoring write cache setting of IDE drive Date: Fri, 28 Jan 2005 22:49:08 +0100 Message-ID: <58cb370e0501281349543d0d14@mail.gmail.com> References: <58cb370e05012813357d42da46@mail.gmail.com> <200501282143.j0SLhqlr022481@falcon10.austin.ibm.com> Reply-To: Bartlomiej Zolnierkiewicz Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from wproxy.gmail.com ([64.233.184.200]:4186 "EHLO wproxy.gmail.com") by vger.kernel.org with ESMTP id S262781AbVA1VtT (ORCPT ); Fri, 28 Jan 2005 16:49:19 -0500 Received: by wproxy.gmail.com with SMTP id 67so319518wri for ; Fri, 28 Jan 2005 13:49:17 -0800 (PST) In-Reply-To: <200501282143.j0SLhqlr022481@falcon10.austin.ibm.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Doug Maxey Cc: Jens Axboe , Jeff Garzik , Linux IDE Mailing List On Fri, 28 Jan 2005 15:43:52 -0600, Doug Maxey wrote: > > On Fri, 28 Jan 2005 22:35:17 +0100, Bartlomiej Zolnierkiewicz wrote: > >On Fri, 28 Jan 2005 15:06:22 -0600, Doug Maxey wrote: > >> > >> On Fri, 28 Jan 2005 20:11:37 +0100, Bartlomiej Zolnierkiewicz wrote: > >> >On Fri, 28 Jan 2005 12:16:01 -0600, Doug Maxey wrote: > >> > > >> >We have too many config options already. > >> > > >> >Behavior should be simple: > >> >* no cache flushes - wcache off by default > >> >* cache flushes - wcache on by default > >> >* inform user about the wcache status > >> >* allow changing of wcache by user > >> > >> My interpretation of what you are saying here is the selection of > >> "cache flush" drives the setting of wcache. Are you saying that > >> "barrier=off" on the boot line the currently (only and will remain) > >> supported method controlling flushes? > > > >No, I am saying that cache flush is a property of disk not fs. > >On the contrary barrier is a property of filesystem. > > Ok. We are talking apples and oranges here. The disk DOES have FLUSH CACHE, > which is the main reason these drives work in the later kernels. You can > switch wcache back and forth, provided that the correct flushing is done. > > Write cache, on the otherhand, which is disabled on the drive by default, > is not honored. What is the practical reason to honor it? > > > >> AFAICS, "barrier=off" just tells the FS (only ext2 and reiser) to not > >> flush writes. I may be misunderstanding how that controls the > >> behavior of the drive at the ll_blk layer. Is that what you want to > >> see a patch to, pick this out of the FS? > > > >No, why? > > > >> >> > >> >> 1) move the cache_write code to ide-io, where it will be callable from > >> >> kernels built without ide-disk. > >> > > >> >I've already pointed this out - this is not needed, you should add > >> >check similar to this for 'xfer_set'. Another reason not to do this > >> >is that write_cache() uses REQ_DRIVE_TASKFILE internally. > >> > >> Is taskfile going away? > > > >Quite the opposite but if you want to use taskfile, map whole > >ide_cmd_ioctl() to it not CACHE_FLUSH_{EXT} command only > >and don't intermix bugfixes with potentially risky changes. > > > > Well, if you turn off write cache, then you must not, at least on these > drives, use FLUSH. All write commands are errored. With the 'drive->wcache' bugfix this shouldn't be a problem as FLUSH commands wouldn't be sent to a drive.