DragonFly kernel List (threaded) for 2006-03
Re: Disk Scheduler
:Has anyone looked at porting over the hybrid disk scheduler stuff that
:was done for freebsd ?
:I'm just now looking at it and I'm having a hard time merging it over
:after the latest buf changes that Matt did.
:Can anyone else take a look at this ? I can post the diffs of what I
:currently have against DragonFly if that would help.
This is a little late, but I have looked at the patch and it
certainly looks interesting. BUT, there are two problems.
First, I do not suggest that anyone attempt to port it due to
the current byte-linearized buffer work that is going on.
Second, unless I am mistaken I do not see any time-domain code
to account for performance issues due to seeking in the HYBRID scheduler
in the patch. For example, if you have two users and each is supposed
to get 50% of available disk bandwidth, and one is running a program
which seeks the disk all over the place while the other is simply
reading a single large linear file, I don't think HYBRID would actually
apportion disk bandwidth properly between the two. To do that properly
would require detecting the situation where the linear reader is
getting less then 50% of the expected (linear) bandwidth and then
forcing some sort of time-domain scheduling for that disk (kinda like
time slices) to prevent the heavy-seeking from destroying performance
for the linear reader.