Re: [9fans] sleep(2) historical question

[Charles Forsyth <charles.forsyth@gmail.com>]

My problem is that the kernel is not currently capable of supplying
what Erik defines, to the process level even internally,
and even for his described applications (delays of a small interval,
tiny retransmission times), it's not clear that the traditional sleep,
which has
*always* been sloppy, is anyway the right model; and certainly not for
any more general application.
I had a quick read through some papers and theses last night, and it
certainly isn't clear cut.

What values could the kernel currently supply to a query interface?
There are no particular bounds
on anything, which was rather my point. I had a similar problem
*inside the kernel* when dealing with
a fast network interface on the Blue Gene.

The whole thing started with an "historical question": "why is
sleep(2) limited to resolution HZ in the portable code? ..."
and I gave what I think is the correct reply historically: "the
relative unimportance of sleep?", but as usual that didn't go down
very well.

For relatively small delays, sleep -> tsleep isn't right. Most of the
ways of making "high-precision" timers available at user level
contain a lot of overhead, or frustration when trying to use them (eg,
POSIX sends a signal, never a harbinger of speed or ease of use).
I've probably just had my fill of general-purpose systems that confuse
"not too often slow" with "timely".

It's less of a problem for Plan 9, than Nix, where I'd like to see any
new things added be sound.

On 29 November 2012 08:12,  <arnold@skeeve.com> wrote:
> Erik's problem boils down to "the kernel knows what it can do and is
> quite capable but i can't get it at from user space".