Re: [9fans] arm & httpd

[erik quanstrom <quanstro@quanstro.net>]

On Mon Nov 18 06:46:22 EST 2013, 9fans@hamnavoe.com wrote:
> > this is because wakeup() takes about 100-1000x as long as sleep(0)
>
> [Citation needed]

since rendezvous has to do a bunch of locks and a context switch,
whereas sleep(0) doesn't really have to do anything other than
check anyhigher(), i thought this wouldn't need proof.

here are some numbers. it turns out my lazy guess was too high,
but the thing to remember is the time wasting and sleep(0) tricks
work because rendezvous is quite slow.

(the test results for semaphore locks vs tas locks were posted to
the list, iirc, and tas locks generally come out on top.  semaphores
get worse as the number of processors increase.)

the rendezvous numbers should be /4 so we have
	time per million
	rendezvous		sleep0
kw	17.71			2.78		6.3
32c intel	1.01			0.14		7.2
4c amd	.785			0.15		5.2

raw data

# arm kirkwood; 1 processor
kw; time 5.rpingpong; time 5.sleep0
4.86u 65.97s 70.84r 	 5.rpingpong
0.61u 2.17s 2.78r 	 5.sleep0

sooner; aux/cpuid -i
       Intel(R) Xeon(R) CPU E5-2470 0 @ 2.30GHz
sooner; wc -l /dev/sysstat
     32 /dev/sysstat
sooner; time 6.rpingpong; time 6.sleep0
0.56u 1.27s 4.04r 	 6.rpingpong
0.05u 0.08s 0.14r 	 6.sleep0
; aux/cpuid -i
AMD Phenom(tm) II X4 965 Processor
; wc -l /dev/sysstat
      4 /dev/sysstat
; time 6.rpingpong;time 6.sleep0
0.25u 1.29s 3.14r 	 6.rpingpong
0.06u 0.08s 0.15r 	 6.sleep0

- erik