On Fri, Dec 07, 2001 at 06:57:39PM +0200, Sami Farin wrote:
> Ahu wrote:
> > Both I think. There are some indications that raising HZ may not work, as it
> > may not raise the resolution of the timers in the Linux Kernel - I am
> > investigating this! So try keeping HZ stable, and raising the size of your
> > bucket.
>
> would it make any difference if you do...
Ok - I've since investigated this. Shapers use timers internally to block
themselves for set periods of time. These timers appear to have HZ
resolution, but a comment in the very good Linux Device Drivers book
http://www.xml.com/ldd/chapter/book/
appeared to indicate that raising HZ would not raise their resolution.
I contacted Jonathan Corbet, one of the authors, and he checked and found
that the book was incorrect: raising HZ *does* increase timer resolution.
> -#define PSCHED_CLOCK_SOURCE PSCHED_JIFFIES
> +#define PSCHED_CLOCK_SOURCE PSCHED_CPU
>
> I didn't see PSCHED_CLOCK_SOURCE in the 2.4routing docs...
> Can you tell more about PSCHED_CLOCK_SOURCE ?
As far as I can see, this only increases the *resolution*, not *precision*.
In other words, you can't specify shorter delays this way but you can
measure a delay that already happened far more precisely.
For example, if you decide to delay for 1 jiffy, 10ms, you may in fact have
waited 14ms. PSCHED_JIFFIES will not see this - 1.4==1 jiffy has passed.
PSCHED_CPU *will* see it, and let the right amount of packets out.
But I'm hoping that Martin Devera can check this for me, devik?
Regards,
bert
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