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

[erik quanstrom <quanstro@quanstro.net>]

On Thu Nov 29 04:20:52 EST 2012, charles.forsyth@gmail.com wrote:
> 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.

i ran a little test.  the meat of the program is this

	cycles(t+0);
	for(i = 0; i < 5000000000ull; i += s)
		nsleep(s);
	cycles(t+1);

	print("%g\n", cyclestoseconds(t[1]-t[0]));

i get quite predictable results; there is no cliff.  

sleep in ns	elapsed time	calculated syscall overhead
1000000000	5.000012		# 2.40µs / syscall
100000000	5.000106		# 2.12µs / syscall
10000000	5.001097		# 2.19µs / syscall
1000000		5.01078		# 2.16µs / syscall
100000		5.102487		# 2.16µs / syscall
10000		6.081568		# 2.16µs / syscall

- erik