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Date:      27 Feb 2002 14:35:29 -0600
From:      Bob Van Valzah <Bob@Talarian.Com>
To:        Kelly Yancey <kbyanc@posi.net>
Cc:        Bruce Evans <bde@zeta.org.au>, Robert Watson <rwatson@FreeBSD.ORG>, Jorge Aldana <jorge@salk.edu>, Garance A Drosihn <drosih@rpi.edu>, smp@FreeBSD.ORG
Subject:   Re: Performance vs. Stable
Message-ID:  <1014842130.2359.113.camel@NewStorm.WhiteBarn.Com>
In-Reply-To: <20020227121320.X8086-100000@gateway.posi.net>
References:  <20020227121320.X8086-100000@gateway.posi.net>

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Maybe Bruce's version of lmbench reports data differently that my (old)
version does? I was surprised by this too so I checked to make sure that
the numbers were absolute. My first round of test showed -CURRENT taking
10 ms while -STABLE took 61 ms for a "null" system call.

Alas when I went to verify my results by rerunning them on -STABLE, I
got different results. In fact, I got 10 ms. I guess I submit a paper to
the Journal of Irreproducible Results (www.jir.com) :-)

So here's the latest run:

		(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     4.7     3.6     3.7  5.6   
8.4    9.9
TwinHead  FreeBSD 4.5-S  233     *10   *1.1K   *5.6K   *9.6K  *38   
*12    *15
TwinHead. FreeBSD 5.0-2  233     *10     1.5     1.3     1.3  1.3   
3.9    7.2

The top line is -CURRENT with WITNESS and friends. The bottom line is
-CURRENT without WITNESS. The middle line is -STABLE.

So the way I'm reading it now is that (once you get WITNESS out of the
way) there's little difference in system call overhead between -STABLE
and -CURRENT. Lmbench "process" numbers seem 30-50% slower on -CURRENT.
The context switch numbers are still 4x to 7x slower on -CURRENT.

I've hooked back up with Larry and will be working with him (and I hope
Bruce Evans) to get a solid version of lmbench and procedures that lead
to more reproducible resutls.

	Bob

On Wed, 2002-02-27 at 14:16, Kelly Yancey wrote:
> On Wed, 27 Feb 2002, Bruce Evans wrote:
> 
> > >
> > >         Processor, Processes - factor slower than the best
> > >         --------------------------------------------------
> >
> > I think you are misinterpreting them.  The non-starrd results are
> > absolute times.  E.g., they say that the "null" syscall takes 6.1 usec
> > in 4.5-S and 6.1 usec in -current.  This is about right.  The "null"
> > syscall is actually a write of 1 byte to /dev/null.  File i/o has been
> > been extensively pessimized in -current using locking.  This only
> > matters much for small i/o's, which is exactly what the benchmark
> > tests.  The pessimization is normally reduced a little for device files
> > by using devfs.
> >
> 
>   I know I am going out on a limb to doubt you, but are you sure?  The chart
> header (as quoted above) sure seems to imply that the starred times are
> absolute and all of the others are relative comparisons.  As such, I was quite
> impressed by how well -current appears to be performing compared to -stable
> given how little optimization has been done so far.
> 
>   Kelly
>   kbyanc@{posi.net,FreeBSD.org}



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