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

Gennady Kupava gb at bsdmn.com
Sun Oct 24 20:10:00 CEST 2010

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:
> > And now, as this conceptual hack put me so high to hall of fame, i
> > consider i can cast 3 simple wishes for qtmoko ;) :
> > 
> > 1. i wish compiled-in guid partition table type into kernel;
> I can try if i find correct config options. If not i'll ask :)


> > 2. i wish xfs module to kernel (as ubifs is comressed fs, it should not
> > eat too much space);
> As module or compiled in?

Module is ok. It's a bit too large to compile in for everyone due to our
128Mb of ram size.

> > 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:

1. Stay more in IDLE state. (less power consumption)
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.

1. Worse granilarity of delays and sheduled works. I think it's
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

I can't 'feel' that something changed.

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

Big thanks to Vasily 'anarsoul' Khoruzhick for patch written on my


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