Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt

Con Kolivas
2005-07-15T04:11:04Z

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On Fri, 15 Jul 2005 09:25, Linus Torvalds wrote:
> On Thu, 14 Jul 2005, Lee Revell wrote:
> > On Thu, 2005-07-14 at 09:37 -0700, Linus Torvalds wrote:
> > > I have to say, this whole thread has been pretty damn worthless in
> > > general in my not-so-humble opinion.
> >
> > This thread has really gone OT, but to revisit the original issue for a
> > bit, are you still unwilling to consider leaving the default HZ at 1000
> > for 2.6.13?
>
> Yes. I see absolutely no point to it until I actually hear people who have
> actually tried some real load that doesn't work. Dammit, I want a real
> user who says that he can noticeable see his DVD stuttering, not some
> theory.

Disclaimer - This is not proof of a real world dvd stuttering, simply a
benchmarked result. My code may be crap, but then the real apps out there may
also be.

Results from interbench v0.21
(http://ck.kolivas.org/apps/interbench/interbench-0.21.tar.bz2)

2.6.13-rc1 on a pentium4 3.06

HZ=1000:
--- Benchmarking Audio in the presence of loads ---
Latency +/- SD (ms) Max Latency % Desired CPU % Deadlines Met
None 0.012 +/- 0.00196 0.021 100 100
Video 1.28 +/- 0.509 2.01 100 100
X 0.289 +/- 0.578 2 100 100
Burn 0.014 +/- 0.002 0.023 100 100
Write 0.025 +/- 0.0349 0.49 100 100
Read 0.02 +/- 0.00383 0.052 100 100
Compile 0.023 +/- 0.00752 0.054 100 100
Memload 0.222 +/- 0.892 9.04 100 100

--- Benchmarking Video in the presence of loads ---
Latency +/- SD (ms) Max Latency % Desired CPU % Deadlines Met
None 0.012 +/- 0.00169 0.023 100 100
X 2.55 +/- 2.37 18.7 100 75.8
Burn 1.08 +/- 1.06 16.7 100 88.2
Write 0.224 +/- 0.215 16.7 100 97.8
Read 0.019 +/- 0.00354 0.059 100 100
Compile 4.55 +/- 4.53 17.6 100 57.5
Memload 1.3 +/- 1.34 51.5 100 88

HZ=250:
--- Benchmarking Audio in the presence of loads ---
Latency +/- SD (ms) Max Latency % Desired CPU % Deadlines Met
None 0.011 +/- 0.00152 0.022 100 100
Video 0.157 +/- 0.398 3.62 100 100
X 1.3 +/- 1.82 4.01 100 100
Burn 0.014 +/- 0.00142 0.026 100 100
Write 0.022 +/- 0.0125 0.092 100 100
Read 0.021 +/- 0.00366 0.048 100 100
Compile 0.03 +/- 0.0469 0.559 100 100
Memload 0.144 +/- 0.681 8.05 100 100

--- Benchmarking Video in the presence of loads ---
Latency +/- SD (ms) Max Latency % Desired CPU % Deadlines Met
None 5 +/- 4.99 16.7 100 54
X 9.98 +/- 8.94 20.7 100 31.2
Burn 16.6 +/- 16.6 16.7 100 0.167
Write 4.11 +/- 4.08 16.7 100 60.8
Read 2.55 +/- 2.53 16.7 100 73.8
Compile 15.6 +/- 15.6 17.7 100 3.5
Memload 2.91 +/- 2.92 45.4 100 72.5

Audio did show slightly larger max latencies but nothing that would be of
significance.

On video, maximum latencies are only slightly larger at HZ 250, all the
desired cpu was achieved, but the average latency and number of missed
deadlines was significantly higher.

Cheers,
Con

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