From owner-freebsd-hackers Mon Aug 31 12:19:38 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id MAA12602 for freebsd-hackers-outgoing; Mon, 31 Aug 1998 12:19:38 -0700 (PDT) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from panzer.plutotech.com (panzer.plutotech.com [206.168.67.125]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id MAA12595 for ; Mon, 31 Aug 1998 12:19:35 -0700 (PDT) (envelope-from ken@panzer.plutotech.com) Received: (from ken@localhost) by panzer.plutotech.com (8.9.1/8.8.5) id NAA07483; Mon, 31 Aug 1998 13:18:16 -0600 (MDT) From: "Kenneth D. Merry" Message-Id: <199808311918.NAA07483@panzer.plutotech.com> Subject: Re: 64k physio limit In-Reply-To: <199808310926.FAA13727@lor.watermarkgroup.com> from Luoqi Chen at "Aug 31, 98 05:26:35 am" To: luoqi@watermarkgroup.com (Luoqi Chen) Date: Mon, 31 Aug 1998 13:18:16 -0600 (MDT) Cc: hackers@FreeBSD.ORG, imp@village.org X-Mailer: ELM [version 2.4ME+ PL28s (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Luoqi Chen wrote... > > Is there any way to get a larger I/O to happen than 64k? I have a tape > > drive that would be happiest if I could do 256kish writes to it at a time, > > rather than only 64k. > > > > Warner > > > Set the device driver's cdevsw:d_maxio to 256k? > > -lq I'm not so sure that will work. physio currently restricts I/O size by using minphys(). minphys() looks at the buffer kva size (b_kvasize), which I think it currently set to MAXPHYS, which is 128K. I think that at least in CAM, you should be able to do 256K writes to a tape drive, assuming: 1. you can get the transactions through to the tape driver's strategy routine in that size and 2. your controller can handle things that size. The first one probably requires changing MAXPHYS, or a buffer chaining scheme. I'm not quite sure what happens if a controller can't handle I/O requests of a particular size. I guess it's handled in the driver, but I've never looked, so I don't know. :) Ken -- Kenneth Merry ken@plutotech.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message