Date: 26 Feb 2002 21:43:45 -0600 From: Bob Van Valzah <Bob@Talarian.Com> To: Robert Watson <rwatson@FreeBSD.ORG> Cc: Jorge Aldana <jorge@salk.edu>, Garance A Drosihn <drosih@rpi.edu>, smp@FreeBSD.ORG Subject: Re: Performance vs. Stable Message-ID: <1014781427.15635.10.camel@Relent.Bob.WhiteBarn.Com> In-Reply-To: <Pine.NEB.3.96L.1020226204912.38595H-100000@fledge.watson.org> References: <Pine.NEB.3.96L.1020226204912.38595H-100000@fledge.watson.org>
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On Tue, 2002-02-26 at 19:50, Robert Watson wrote:
> It's worth noting that WITNESS can have a dramatic impact on performance.
> I actually turned it off by default recently, and it got turned back on
> again (for good reasons). Any benchmarking must be done without those
> settings turned on.
Allow me to quantify the difference and show a more valid comparison to
-STABLE as well.
(Best numbers are starred, i.e., *123)
Processor, Processes - factor slower than the best
--------------------------------------------------
Host OS Mhz Null Null Simple /bin/sh Mmap 2-proc
8-proc
Syscall Process Process Process lat
ctxsw ctxsw
--------- ------------- ---- ------- ------- ------- ------- ---- ------
------
TH.Witnes FreeBSD 5.0-2 232 11 3.1 2.8 2.8 4.2
3.7 4.9
TwinHead FreeBSD 4.5-S 228 6.1 2.2 1.9 1.9 2.4
*27 *30
TwinHead. FreeBSD 5.0-2 233 *10 *1.7K *7.3K *12.6K *51
1.7 3.6
The top line is -CURRENT with WITNESS and friends turn on. The bottom
line is -CURRENT with them turned off. The middle line is -STABLE.
I'm surprised by the results here. (Maybe I'm misinterpreting them?) It
looks like -CURRENT is over 6x faster than -STABLE on null system calls.
Forks and mmap seem about 2x faster but context switches are slower.
It's interesting to note that WITNESS and friends slowed down null
system calls by 11x and other kernel operations by about 3-5x.
Bob
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