HZ value change groundings (Was: jitterless touchscreen input in .34)

Riccardo Magliocchetti riccardo.magliocchetti at gmail.com
Mon Oct 25 09:15:13 CEST 2010

Il 24/10/2010 20:10, Gennady Kupava ha scritto:
> В Вск, 24/10/2010 в 19:34 +0200, Radek Polak пишет:
>> You wrote:>  В Чтв, 21/10/2010 в 22:04 +0200, Radek Polak пишет:
>>> 3. i wish 100HZ patch included to qtmoko
>>> (http://www.bsdmn.com/openmoko/kernel/0001-Use-100-as-HZ-value-on-S3C24XX.p
>>> atch)
>> Oki, i can try, is there any description for the patch? E.g. What does it do
>> and how can i test it?
> It does simple thing - change HZ value of linux kernel from 200HZ to
> 100HZ. Main reason is performance.
> My rationale is following:
> Basically this mean that timer interrupts amount will be reduced from
> 200 per second to 100 per second. This allows:
> Pros:
> 1. Stay more in IDLE state. (less power consumption)

I think that this is something that would be more noticeable with Vasily's

> 2. If several tasks are active, do 2 times less context switches (and
> our context switches are expensive). Do not think it will be 'slow'.
> This is not applied to all tasks - but only to CPU bound ones.
> 3. Less interrupts is good on it's own.
> Cons:
> 1. Worse granilarity of delays and sheduled works. I think it's
> impossible
> 2. May reveal some bugs, as any new non-trivial system-wide change.
> Basically it works here, but i didn't test everything.
> Other arguments:
> I checked other boards config files and it turned out that only few of
> them (10% or so) using 200 as HZ value.
> I did lmbenching and found that difference is few percent, but still
> noticeable.
> I can't 'feel' that something changed.

Has anyone investigated gathering some data with ftrace? examples start 
from line 246.


> So, this patch is just sets new value for HZ and changes s3c timer
> interrupt frequency.

Wouldn't something like that in arch/arm/Kconfig avoid changes in 

default 100 if ARCH_S3C2410

Just asking :)


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