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SubjectRe: Task queue makes slow device even slower
Date
Hello!

> As a long-term solution, perhaps something along the lines of the "soft
> timers" described in http://www.cs.rice.edu/~aron/papers/soft-timers.ps.gz
> might be useful for many cases where we have udelays or even mdelays
> today.

Soft timers _are_ _implemented_ in linux from the very beginning
and called BHs. Anyone who wants polling may hook them and poll.
Essentially, packet scheduler in 2.2 uses soft timers, with events
generated by net, system scheduler and timer.

I remember I've already said you and Jamal that I tried to add more events
to soft timers in packet scheduler and the result was disguisting,
they eat gobs of cpu and however inappropriate for real time tasks.

From the other hand, true variable resulution timer is possible
and Ingo said he is ready to complete it.


What's about the paper. I read it not enough carefully, and, probably,
it is the reason why I understood almost nothing. Seems, the experimental
results summarized there are not quite legal. F.e. the thing puzzled me
is increasing throughput on high delay*throuput pipes. It is the only
place where timed TCP transmission have a sense, but they did no experiments
emulating fat pipe and used normal one... Seems, in this case all the effect
is achieved because disabling slow start. Well, seems, I have to read
it more carefully.

Alexey Kuznetsov

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