Date: Sat, 3 Feb 2001 13:23:14 -0800 (PST)
From: Matthew Jacob <mjacob@feral.com>
To: "Justin T. Gibbs" <gibbs@scsiguy.com>
Cc: Matt Dillon <dillon@earth.backplane.com>, Mike Smith <msmith@FreeBSD.ORG>, Dag-Erling Smorgrav <des@ofug.org>, Dan Nelson <dnelson@emsphone.com>, Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp>, arch@FreeBSD.ORG
Subject: Re: Bumping up {MAX,DFLT}*PHYS (was Re: Bumping up {MAX,DFL}*SIZ in i386)
Message-ID: <Pine.LNX.4.21.0102031323080.27128-100000@zeppo.feral.com>
In-Reply-To: <200102032103.f13L3nO55354@aslan.scsiguy.com>
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Thank you. You put it exactly right. > > And, finally, while large I/O's may seem to be a good idea, they can > > actually interfere with the time-share mechanisms that smooth system > > operation. > > Large I/Os, while interesting for disks, are often *required* for dealing > with non-disk devices. If I want to read a tape generated from an SGI, > for example, the records may be 1MB in size. Almost all of our PCI SCSI > controllers can perform such a large I/O, but DFLTPHYS prevents you from > servicing such an I/O. On devices like tape, you can't break up the I/O > to the device into chunks smaller than the block size. We *need* a way > to perform I/Os that span more than one buffer so we can avoid the DFLTPHYS > limit. > > -- > Justin > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-arch" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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