Date: Tue, 19 Feb 2002 16:36:09 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Jeff Roberson <jroberson@chesapeake.net> Cc: Julian Elischer <julian@elischer.org>, arch@FreeBSD.ORG Subject: Re: Prioritized bio patches. (Updated patch) Message-ID: <200202200036.g1K0a9U64733@apollo.backplane.com> References: <20020219171504.T12686-100000@mail.chesapeake.net>
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:First of all, I updated the patch. When I merged it in from our sources I
:missed a one line change that fixed a race condition. I also changed the
:priority level of NORMAL to 6 so that I could avoid all of the -1's to
:index the low priority queue.
:
:Secondly, I ran a simple test of a kernel compile. The test system has
:one disk. I did a dd of /dev/zero to a file in a users home directory
:with a nice of 20 while doing a kernel compile. The original compile took
:11 minutes and 32 seconds. The compile with the dd going took 15 minutes
:and 12 seconds.
:
:I originally did this work for VOD server. The idea being that the VOD
:data was guaranteed and the rest of the system would just have to wait.
:...
:
:Jeff
Jeff, this looks like really interesting stuff! Could you explain
the starvation issues in more depth? e.g. if I have a nice+20 process
doing disk I/O and a nice-20 process saturating the disk, is it possible
for the nice-20 process to lockout the nice+20 process from doing
any disk I/O?
Another worry: what happens when a low priority process is holding a
vnode lock while doing synchronous I/O and a high priority process wants
to access the same vnode? Here I am specifically thinking about
directory accesses that are incidental to a path lookup.
-Matt
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