Date: Thu, 02 Dec 1999 22:32:36 -0800 From: Mike Smith <msmith@freebsd.org> To: mjacob@feral.com Cc: Stephen McKay <syssgm@detir.qld.gov.au>, Mike Smith <msmith@FreeBSD.ORG>, freebsd-scsi@FreeBSD.ORG Subject: Re: Tape driver problems Message-ID: <199912030632.WAA05573@mass.cdrom.com> In-Reply-To: Your message of "Thu, 02 Dec 1999 22:17:51 PST." <Pine.BSF.4.10.9912022217210.23244-100000@beppo.feral.com>
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> > On Thursday, 2nd December 1999, Mike Smith wrote: > > > > >Either the aha code needs to be fixed to allow more s/g entries, or the > > >bounce buffer code needs to be fixed to allocate things in larger chunks > > >and thus keep fragmentation down, or we should just abandon these useless > > >10-year-old ISA SCSI controllers and worry about more useful things. 8) > > > > Well, I'm for changing the buffer code or the aha code, whichever makes > > the most sense at the time. Unfortunately I don't know that bit of the > > kernel yet. But I will eventually work it out because I have too many old > > ISA SCSI cards to take you up on your last suggestion. > > See other mail. I still believe that the AHA driver should work better, > but it's a low priority item now. This particular issue is a defect in the bounce-buffering code; the 1542 is limited to 16 or maybe 17 s/g entries. (We allow 17, the Linux driver stops at 16.) This isn't an issue for most things until you get up near 64k, where fragmentation lets you run out of page-sized entries. I'm not sure how best we could work around this without clustering pages in bounce-buffer memory. If you've got any neat ideas I'll happily file them for next time someone goes looking at that code. -- \\ Give a man a fish, and you feed him for a day. \\ Mike Smith \\ Tell him he should learn how to fish himself, \\ msmith@freebsd.org \\ and he'll hate you for a lifetime. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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