From owner-freebsd-arch  Fri Jul  7 13:18:13 2000
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To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: Alfred Perlstein <bright@wintelcom.net>,
	Marius Bendiksen <mbendiks@eunet.no>,
	Bill Fumerola <billf@chimesnet.com>, freebsd-arch@freebsd.org
Subject: Re: Alterations to vops 
From: Chuck Paterson <cp@bsdi.com>
Date: Fri, 07 Jul 2000 14:16:18 -0600
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Matthew Dillon wrote on: Fri, 07 Jul 2000 12:50:11 PDT
}
}    Programs such as cvsup and find do not queue up billions of
}    I/O's.  They queue up one at a time pretty much, but the I/O's
}    generate a lot of seeking due to the directory layouts on the
}    media (when you have lots of small directories).  
}
}					-Matt
}					Matthew Dillon 
}					<dillon@backplane.com>
}
}


	If for whatever reason part of your vm working gets
paged out or has to be repaged in from an executable the
system can have really bad user response. As Matt points
out there aren't bunches of I/O queued from these processes,
but you are still screwed. The process you are interested in
gets to do one paging operation and then all other processes
get to do one of there I/O operations. If there are a couple
of processes running in the background then the disk ends
up doing several seeks for every page your interactive process
needs filled.

Chuck


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