FreeBSD 5.3 I/O Performance / Linux 2.6.10 | Continued Discussion

Nick Pavlica linicks at
Thu Jan 27 17:04:32 PST 2005

> The move to an MPSAFE VFS will help with that a lot, I should think.

Do you know if this will find it's way to 5.x in the near future? 

> Also, while on face value this may seem odd, could you try the following
> additional variables:
> - Layer the test UFS partition directly over ad0 instead of ad0s1a
> - UFS1 vs UFS2

I just tested with UFS1 and had almost the exact same results.

> Finally, in as much as is possible, make sure that the layout of the disks
> is approximately the same -- as countless benchmarking papers show, there
> are substantial differences (10%+) in I/O throughput depending on where on
> the disk surface operations occur.  That's one of the reasons to try UFS1
> for the test partition, although not the only one.

My tests use the exact same disk layout, and hardware.  However, I
have had consistent results on all 4 boxes that I have tested on.

At this point I'm making the assumption that the poor disk I/O
performance on 5.3 isn't a file system issue, but is tied to a larger
issue with the Kernel (I know never make assumptions ... :)).  In all
my testing, I have noticed that 5.3 doesn't appear to release cpu
resources even if there isn't any other demand for resources.  I would
compare it to driveling a car with a governor on it.  When I tested
with 4.11, it allocated considerably more resources.  I do hope that
the 5.x issues are resolved soon so that I can deploy may production
servers on it rather than starting on 4 and them making the big
switch.  I will probably test 6 for the fun of it.

--Nick Pavlica

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