Re: "no hz"/"dynamic tick" option and TC/TBF (token bucket filter)behaviour...

[Patrick McHardy]

leon zadorin wrote:
> 2) for kernels which do have the aforementioned option enabled: how
> does this affect the "tc" (traffic control) utility and the Token
> Bucket Filter (tbf) queueing discipline (traffic-smoothing)
> behhaviour?
> 
> For example, the TBF doco suggests that due to the whole fixed Hz
> thing in the kernel (e.g. 100Hz) the maximum rate of the TBF would
> actually be limited to say 1mbit on Intel arch (with the default
> mtu... but if mtu is incleased, so is the burstiness of the traffic
> which is what TBF is trying to prevent in my deployment scenarios).
> ...
> 
> So what about the kernels which use this "dyna tick" option - in such
> a kernel, will there be an interrupt generated (e.g. at microsec.
> precision on most platforms) for every packet's send time (e.g. say at
> TBF's rate is at 25Mbps and one sends out 1KB data packets... will
> there be  an interrput generated every... 300 microseconds?)...


No, it doesn't affect the timer resolution. net-2.6.22 includes
patches that switch all qdiscs to hrtimers, which allows to use
much smaller burst rates.

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