Subject: Re: O_ASYNC on ttys
To: None <>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-kern
Date: 07/09/2001 19:00:26
>>> then started dumping characters at it.  Of course, they came back
>>> at 240Hz, just as I wanted.
>>> I'm surprized that works.  Are you sure you're getting 240Hz
>>> wakeups?
(As I think I said, yes, I am.  Instrumenting the code indicates
235-245 wakeups per second, from a userland POV.)
>> [W]ith low speed i think serial port sends one interrupt per
>> character.  so why it shouldn't work?
> Because there's a difference between 240 interrupts per second and
> 240 wakeups per second.  The difference is the scheduler.

Yes, that concerned me a little.  Fortunately the concern seems to have
been unnecessary; as I indicated, I was getting just about 240Hz
wakeups in userland.

> If one tick is 10 ms (100 Hz), and there's a process running when the
> interrupt comes it, there's a good chance the process running will
> get to finish its tick.

This is not an issue for my application; performance with other
processes wanting the CPU is not expected to be acceptable (though it
would be Cool if it were).

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