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Description: Ubuntu oneiric (development branch)
Release: 11.10
By default, or at least what is default on my machine the ondemand governor has
the sampling_down_factor set to 1. In testing this seems to show that the turbo
boost on my Intel CPU never gets a chance to boost up properly.
It seems by the time you set it to about 10, turbo can work as expected,
with only a minor increase in speed above that. This problem only seems
to appear, or becomes more apparent once the CPU has had its turbo
overclocked a few multipliers above stock.
Looking at the current scaling frequency you can see with a
sampling_down_factor setting of 1 that it keeps jumping between 1600Mhz
and the max freq, with higher settings it is static.
eg:-
cat /sys/devices/system/cpu/cpu*/ondemand/sampling_down_factor
1
Start of PI calculation up to 1048576 decimal digits
End of initialization. Time= 0.168 Sec.
I= 1 L= 0 Time= 0.492 Sec.
I= 2 L= 0 Time= 0.568 Sec.
I= 3 L= 1 Time= 0.552 Sec.
I= 4 L= 2 Time= 0.568 Sec.
I= 5 L= 5 Time= 0.560 Sec.
I= 6 L= 10 Time= 0.560 Sec.
I= 7 L= 21 Time= 0.560 Sec.
I= 8 L= 43 Time= 0.560 Sec.
I= 9 L= 87 Time= 0.568 Sec.
I=10 L= 174 Time= 0.556 Sec.
I=11 L= 349 Time= 0.568 Sec.
I=12 L= 698 Time= 0.556 Sec.
I=13 L= 1396 Time= 0.556 Sec.
I=14 L= 2794 Time= 0.564 Sec.
I=15 L= 5588 Time= 0.556 Sec.
I=16 L= 11176 Time= 0.556 Sec.
I=17 L= 22353 Time= 0.540 Sec.
I=18 L= 44707 Time= 0.524 Sec.
I=19 L= 89415 Time= 0.488 Sec.
End of main loop
End of calculation. Time= 11.041 Sec.
End of data output. Time= 0.068 Sec.
Total calculation(I/O) time= 11.109( 0.356) Sec.
echo 10 > /sys/devices/system/cpu/cpu*/ondemand/sampling_down_factor
------ Started super_pi run : Thu Sep 29 22:04:10 BST 2011
Start of PI calculation up to 1048576 decimal digits
End of initialization. Time= 0.124 Sec.
I= 1 L= 0 Time= 0.356 Sec.
I= 2 L= 0 Time= 0.404 Sec.
I= 3 L= 1 Time= 0.396 Sec.
I= 4 L= 2 Time= 0.404 Sec.
I= 5 L= 5 Time= 0.400 Sec.
I= 6 L= 10 Time= 0.396 Sec.
I= 7 L= 21 Time= 0.404 Sec.
I= 8 L= 43 Time= 0.400 Sec.
I= 9 L= 87 Time= 0.400 Sec.
I=10 L= 174 Time= 0.400 Sec.
I=11 L= 349 Time= 0.400 Sec.
I=12 L= 698 Time= 0.396 Sec.
I=13 L= 1396 Time= 0.404 Sec.
I=14 L= 2794 Time= 0.400 Sec.
I=15 L= 5588 Time= 0.392 Sec.
I=16 L= 11176 Time= 0.400 Sec.
I=17 L= 22353 Time= 0.388 Sec.
I=18 L= 44707 Time= 0.372 Sec.
I=19 L= 89415 Time= 0.340 Sec.
End of main loop
End of calculation. Time= 7.884 Sec.
End of data output. Time= 0.052 Sec.
Total calculation(I/O) time= 7.936( 0.284) Sec.
echo 100 > /sys/devices/system/cpu/cpu*/ondemand/sampling_down_factor
Start of PI calculation up to 1048576 decimal digits
End of initialization. Time= 0.120 Sec.
I= 1 L= 0 Time= 0.336 Sec.
I= 2 L= 0 Time= 0.380 Sec.
I= 3 L= 1 Time= 0.392 Sec.
I= 4 L= 2 Time= 0.384 Sec.
I= 5 L= 5 Time= 0.384 Sec.
I= 6 L= 10 Time= 0.384 Sec.
I= 7 L= 21 Time= 0.384 Sec.
I= 8 L= 43 Time= 0.380 Sec.
I= 9 L= 87 Time= 0.384 Sec.
I=10 L= 174 Time= 0.380 Sec.
I=11 L= 349 Time= 0.388 Sec.
I=12 L= 698 Time= 0.380 Sec.
I=13 L= 1396 Time= 0.380 Sec.
I=14 L= 2794 Time= 0.384 Sec.
I=15 L= 5588 Time= 0.376 Sec.
I=16 L= 11176 Time= 0.380 Sec.
I=17 L= 22353 Time= 0.364 Sec.
I=18 L= 44707 Time= 0.356 Sec.
I=19 L= 89415 Time= 0.336 Sec.
End of main loop
End of calculation. Time= 7.540 Sec.
End of data output. Time= 0.044 Sec.
Total calculation(I/O) time= 7.584( 0.276) Sec.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: Confirmed
--
Default sampling_down_factor setting for ondemand governor cripples Intel turbo
boost
https://bugs.launchpad.net/bugs/862785
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