Messages in this thread | | | Date | Wed, 19 Feb 2014 19:17:17 +0000 | From | One Thousand Gnomes <> | Subject | Re: locking changes in tty broke low latency feature |
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> How can the requirement be for both must-handle-in-minimum-time data > (low_latency) and the-userspace-reader-isn't-reading-fast-enough- > so-its-ok-to-halt-transmission ?
Because low latency is about *turn around* time. There are plenty of protocols that can flow control, do flow control and want low latency because they are not windowed. It's not mutually exclusive by any means.
> But first I'd like some hard data on whether or not a low latency > mode is even necessary (at least for user-space).
The easy way to simulate the annoying as crap worst cases from dumbass firmware downloaders and the like is to set up a link between two PCs and time 2000+ repetitions of
send 64 bytes wait for a Y send 64 bytes wait for a Y ....
and the matching far end being a box running an existing kernel or a PIC or something doing the responses.
Historically we used to lose about 20mS per cycle which over 2000 got to be a bit of a PITA.
Low latency goes back to the days of flip buffers, bottom halves an a 100Hz clock. There are certainly better ways to do it now if its needed.
Alan
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