Sidebar on expected performance (was: can I let all winbindd processes accept connections like nginx does)

[David Collier-Brown]

On 12/17/2013 10:11 AM, Tom wrote:
> Volker, appreciate your help!
>>> Since you said DC is bottleneck, then in your experience,
>>> generally how many NTLM authentications that winbindd can
>>> handle per second, wthat's the expected performance?(seems
>>> 300/s is small....)
If you know how long a single operation does on a non-loaded system with
the cache warmed up, etc, then that "response time measurement is a good
estimate of the "service time" of the program,from which you can draw a
pretty-worst-case load graph.

If we were to pretend 300 authentications per second is typical of a
low-load system (boy is it not!), then on a uniprocessor one
authentication takes 0.003 seconds. Assigning a sleep time of 0.99 to
make 1 user == 1 authorization/second you get the attached performance
(slowdown) curve.

For people on the list, who probably won't get the gif, the response
times predicted by this example are an "_/" shaped curve, turning
upwards at 300 authentications/second

General closed solution from PDQ where serviceDemand = 0.003, centers =
1, think time = 0.996 dmax = 0,
Load Response
100, 0.004259
200, 0.007332
300, 0.022343
400, 0.204035 -- things start getting seriously bad about here
500, 0.504000
600, 0.804000
700, 1.104000
800, 1.404000
900, 1.704000
1000, 2.004000

If you can capture a service time at low utilization, I'll generate you
a predicted curve, and we can use that to test if we get the expected
performance, and if not, why not.

--dave

-- 
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb at spamcop.net           |                      -- Mark Twain
(416) 223-8968

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