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Date:      Sat, 18 Jun 2011 17:21:38 +0200
From:      Ivan Voras <ivoras@freebsd.org>
To:        freebsd-arch@freebsd.org
Subject:   Re: [RFC] shipping kernels with default modules?
Message-ID:  <itifq0$s6n$1@dough.gmane.org>
In-Reply-To: <4DF3D4EB.5030805@FreeBSD.org>
References:  <BANLkTin2AwKRT7N6HWqBctJcT72_mR=Otg@mail.gmail.com>	<4DF3B532.6020908@FreeBSD.org>	<D76B9160-327F-454F-AAD2-567D837BCD68@bsdimp.com>	<20110611201703.GO48734@deviant.kiev.zoral.com.ua> <4DF3D4EB.5030805@FreeBSD.org>

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On 11/06/2011 22:49, Doug Barton wrote:

> And no one has ever been surprised that assumptions proved invalid in
> the light of actual testing? :)  Theorizing on this point is of
> less-than-zero utility. Who is going to volunteer to do the actual
> benchmarking?

For what it's worth, I've done the comparison with GEOM_ZERO and
"diskinfo -vt". The results are surprising. I've done about 7 iterations
of the diskinfo benchmark in each case (module and compiled-in) and
analyzed all their outputs collectively with ministat - as there is no
actually IO performed, all operations are basically NOPs no matter what
seeks are issued.

Here's the ministat analysis of "seek times" (x is as module, + is as
directly compiled; GENERIC is used in both cases, AMD64 8.2-RELEASE):

x  70         0.021         0.031         0.028   0.027585714  0.0016637034
+  98         0.025         0.033         0.031    0.02972449  0.0020548189
Difference at 95.0% confidence
        0.00213878 +/- 0.000583402
        7.7532% +/- 2.11487%
        (Student's t, pooled s = 0.00190204)


Here's the analysis for bandwidth part of the benchmark (same symbols):

    N           Min           Max        Median           Avg        Stddev
x  30       1785465       2096170       1909806     1915060.4     77626.781
+  42       1777623       2083800       1819215     1833298.4     62484.689
Difference at 95.0% confidence
        -81761.9 +/- 32966.2
        -4.26942% +/- 1.72142%
        (Student's t, pooled s = 69161.2)


It looks like for both benchmarks, the results are better for the module
case (lower seek times, higher bandwidth).

As the results were surprising, I did ABAB interleaving of the two cases
(module vs built-in).




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