Re: SMP on FreeBSD 6.x and 7.0: Worth doing?

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.

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.

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. 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.)

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.
(Networking does not seem to be the botteneck, though I have heard that the
IP stack in 7-CURRENT needs optimization and that this had been proposed as
a sponsored project.)

--Brett

P.S. -- If the chip manufacturers were not making it so that one needs to
go to SMP to get more processing power, I wouldn't be doing SMP. I'd rather
use FreeBSD 4.11 on a single core "gaming" CPU, as I did a few years ago
when I needed a very fast server. But this isn't a viable option nowadays....

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