Brett Glass wrote:
At 07:14 AM 12/24/2007, Scott Long wrote:
Brett,
There could be several problems here:
1. WITNESS, INVARIANTS, malloc debugging. Are any of these turned on for you?
I don't recall if malloc debugging got turned off yet for the
7.0 snapshots.
I nuked debugging when I recompiled the kernel with SCHED_ULE.
Did you also nuke malloc debugging?
2. Disk subsystem. What kind of disk controller are you using? Not all
drivers work well in FreeBSD. Are linux and freebsd using identical
hardware?
They were. The drives are SATA.
Connected to what controller?
3. Directory hashing. If you're using squid, you __must__ tune the DIRHASH,
otherwise you'll spend a lot of time doing pathname lookups. What filesystem is
linux using?
Whatever comes standard with Ubuntu.
Which is???
As for directory hashing: Squid doesn't
use more than 256 entries in each one, so that's what I normally set. I
also normally do a newfs with parameters that favor the distribution of
object sizes found in Web caches. (We did this on both Linux and FreeBSD.)
newfs tuning has little to do with this.
Would you mind if I logged into your test system and looked around to
help diagnose the problem?
The system isn't online now, because it's been a week since the tests and
I also wanted to try the 6.3 beta and a few hardware changes.
My guess, based on what I saw, is that UFS2 doesn't take as much advantage of
SMP as Linux's file system does and threads are blocking on file I/O.
That's really just speculation on your part, though. UFS is SMP
capable, but there really are a whole lot of factors that some into
play here so it's really hard to speculate with any chance of success.
I can tell you from my experience that a thrashed namei cache looks a
lot like slow disk I/O to the casual observer, and that tuning the
dirhash is highly important. Thus why I'd like to help out here and
see for myself what is going on.
Scott
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