Date: Mon, 31 Aug 1998 12:07:24 +0000 From: Mike Smith <mike@smith.net.au> To: Joao Carlos Mendes Luis <jonny@jonny.eng.br> Cc: luoqi@watermarkgroup.com (Luoqi Chen), hackers@FreeBSD.ORG, imp@village.org Subject: Re: 64k physio limit Message-ID: <199808311207.MAA00438@dingo.cdrom.com> In-Reply-To: Your message of "Mon, 31 Aug 1998 15:34:22 -0300." <199808311834.PAA17561@roma.coe.ufrj.br>
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> #define quoting(Luoqi Chen) > // > 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? > > Which problems arise from making this the default ? Memory waste ? Drivers may expect not to be called with more than 64k of work at a given time. Having a single limit anywhere is bogus; the d_maxio field should be used and fragmentation managed at a higher level. I don't recall whether this is now being done correctly; it wasn't working properly when I had to fix the 'wfd' driver to deal with the Zip not supporting > 32k transfers. I don't know of any driver that maintains a maximum-transfer sized buffer, no. -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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