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[Bug 862785] Re: Default sampling_down_factor setting for ondemand governor cripples Intel turbo boost

To: kernel-packages@xxxxxxxxxxxxxxxxxxx
From: Launchpad Bug Tracker <862785@xxxxxxxxxxxxxxxxxx>
Date: Thu, 13 Feb 2014 04:18:31 -0000
Reply-to: Bug 862785 <862785@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx
[Expired for linux (Ubuntu) because there has been no activity for 60
days.]

** Changed in: linux (Ubuntu)
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/862785

Title:
  Default sampling_down_factor setting for ondemand governor cripples
  Intel turbo boost

Status in “linux” package in Ubuntu:
  Expired

Bug description:
  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.

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