Subject: Re: O_ASYNC on ttys
To: None <firstname.lastname@example.org>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
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
(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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