On Tue, Nov 18, 2008 at 7:14 PM, Gerrit Renker <gerrit@xxxxxxxxxxxxxx> wrote: > | The RFC uses an example of 1 msec scheduling and 0.1 msec RTT. However > | what would be worse is devices on a LAN with 10 msec timer - e.g. two > | embedded devices at home - I haven't done the maths but I think the > | rate achievable would be quite low. > If we use lower-resolution timers I think there should be a > recommendation (in the Kconfig menu for instance) not to use > low HZ values. > > Previously this was done as a build warning, but it is annoying if > people do an allmodconfig and are not otherwise interested in DCCP. > Agree > Do you think we could live with clamping the RTT to some sensible > minimum, since on a local LAN the use of congestion control is > questionable? I was thinking in the order of 0.5 ... 1msec. > I think that is a good idea - if 1 msec, and HZ = 1000 then we wouldn't lose any transmission capability. > | Thinking laterally there is another possible solution - something I > | used way back in the 80s for another project - build your own > | scheduler! We could set a high resolution timer to tick every 0.1 msec > | and then use the coarse grained algorithm at that point.... > | > So we have three possible options - timer-based (low/high), and your > suggestion above. We can keep these variants open by spawning an > experimental subtree which provides an alternative implementation, so > that people could explore alternative algorithms, compare and send patches. > > For production use the low-resolution variant is the simplest and less > expensive option, and it is good that there is consensus about it. > Yes - and with your RTT clamping then no need to do my idea around scheduler. > In a discussion about two years ago there was another > idea, doing away with the nofeedback timer, by checking the nofeedback > time at the instant a packet is sent. > I think this is useful as reduces the amount of timers going off, which reduces system load. -- Web: http://wand.net.nz/~iam4/, http://www.jandi.co.nz Blog: http://iansblog.jandi.co.nz
