From owner-freebsd-smp  Tue Feb 26 20: 2:14 2002
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Subject: Re: Performance vs. Stable
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
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Date: 26 Feb 2002 22:02:05 -0600
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On Tue, 2002-02-26 at 21:50, Robert Watson wrote:
> 
> On 26 Feb 2002, Bob Van Valzah wrote:
> 
> > 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. 
> 
> What is the 'null system call'?

The cop-out answer: I don't write the benchmarks, I just run them :-)

Seriously, I was wondering that myself, but I hadn't bothered to look it
up till you asked. Consulting the manpage:

	http://www.bitmover.com/lmbench/lat_syscall.8.html

It looks like Larry was a bit fast and loose with language in writing
the summary report (maybe to make it fit in the header). It appears to
be the time needed to write one byte to /dev/null. I don't see why
that's any more "null" than say, getpid().

	Bob


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