> > Using iorate.c, I guess somewhat different numbers for the 2.6.15
> > kernel than
> > for the 2.6.8 kernel - the 2.6.15 kernel starts off at 105MB/s and
> > head down
> > to 94MB/s, while 2.6.8 starts at 140MB/s and heads town to 128MB/s.
> >
> > That seems like a significant difference to me?
yes that's surprising. I should have mentioned that the way I normally
use iorate output is to plot the incremental bandwidth as a function of
position (disk offset). that way I can clearly see contributions of
kernel page-cache, possible flattening due to a bottleneck, and the normal
zoned-recording curve.
#!/usr/bin/perl
use strict;
for my $fname (@ARGV) {
open(I,"<$fname");
open(INC,">$fname.inc");
open(AVG,">$fname.avg");
while (<I>) {
my @fields = split;
if ($#fields == 3 && /[0-9]$/) {
print INC "$fields[1] $fields[2]\n";
print AVG "$fields[1] $fields[3]\n";
}
}
close(AVG);
close(INC);
}
I sometimes plot the running average curve as well, since it shows how much
less informative the average (ala bonnie/iozone/etc) is.
> Keep in mind that disk performance is very dependent on exactly what
> your IO pattern looks like and which part of the disk you are reading.
that's the main point of using iorate.
> We have some tests that we use to measure raw disk performance that try
> to get through these hurdles to measure performance in a consistent and
> reproducible way...
iorate profiles are reasonably consistent, as well. it doesn't attempt to
do any IO pattern except streaming reads or writes.
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