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

[Con Kolivas]

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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