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Tasklist

FS#7195 - change kernel options

Attached to Project: Arch Linux
Opened by Roberto Spadim (rspadim) - Thursday, 17 May 2007, 20:38 GMT
Last edited by Tobias Powalowski (tpowa) - Friday, 25 May 2007, 16:58 GMT
Task Type Feature Request
Category Kernel
Status Closed
Assigned To Tobias Powalowski (tpowa)
Architecture All
Severity Medium
Priority Normal
Reported Version 2007.05 Duke
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No

Details

could we change kernel timer from 250hz to 1khz?
this could return more precise values for timing, a bit overload on very big systems but no big performace loss

and using jack server can be done without recompiling kernel for realtime timing
This task depends upon

Closed by  Tobias Powalowski (tpowa)
Friday, 25 May 2007, 16:58 GMT
Reason for closing:  Won't implement
Comment by Roman Kyrylych (Romashka) - Thursday, 17 May 2007, 22:21 GMT
No! This is a bad idea IMO.
But I think we should change to 300Hz.
Quote:
It is useful to have 300Hz support when doing multimedia work: 250 is fine for us in Europe but the US frame rate is 30fps (29.99 blah for pedants). 300 gives us a tick divisible by both 25 and 30, and for interlace work 50 and 60. It's also giving similar performance to 250Hz
Comment by Jan de Groot (JGC) - Thursday, 17 May 2007, 22:26 GMT
Is this still an issue with a tickless timer kernel?
Comment by Roman Kyrylych (Romashka) - Thursday, 17 May 2007, 22:30 GMT
I don't know.
Here's what we have in the latest kernel config:

#
# Processor type and features
#
CONFIG_TICK_ONESHOT=y
CONFIG_NO_HZ=y
CONFIG_HIGH_RES_TIMERS=y
.
.
.
#
# Firmware Drivers
#
.
.
.
# CONFIG_HZ_100 is not set
CONFIG_HZ_250=y
# CONFIG_HZ_300 is not set
# CONFIG_HZ_1000 is not set
CONFIG_HZ=250
Comment by Roberto Spadim (rspadim) - Friday, 18 May 2007, 14:24 GMT
why not 1000? jack server run very well with 1000
1k work ok with my tv card too
Comment by Roberto Spadim (rspadim) - Friday, 18 May 2007, 14:24 GMT
i didn't tested performace on very big mysql database running many queries, or an big apache with many requests
Comment by Roman Kyrylych (Romashka) - Friday, 18 May 2007, 14:52 GMT
or a laptop
Comment by Roberto Spadim (rspadim) - Friday, 18 May 2007, 15:05 GMT
we have some scenarios to optmize arch linux
laptop (power consumition must be near 0 watt/hour)
server (process and memory access for background programs must be real time, to allow fast return to clients, no power problems)
desktop (xorg, alsa, and other multimedia devices must run very fast, no power problems)

are config_hz a source of power problem for laptops?
what about server and desktop performace?
Comment by Jan de Groot (JGC) - Wednesday, 23 May 2007, 17:48 GMT
100 Hz is good for servers, as your server should be doing its tasks, it shouldn't be interrupted 1000 times per second because of a useless timer interrupt. 250Hz is a value chosen by linux developers as a compromize between servers (100Hz) and desktops (1000Hz). You can't put this value at any random number because things in the kernel depend on timings. Putting it to 500 because you like the number will kill a lot of things (that's why there's CONFIG_HZ100, CONFIG_HZ250, etc, sources have ifdefs for that).
Comment by Roberto Spadim (rspadim) - Wednesday, 23 May 2007, 18:22 GMT
archlinux is otimized for what use? desktop?
Comment by Tobias Powalowski (tpowa) - Friday, 25 May 2007, 16:58 GMT
we stay with default hz by kernel devs

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