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SubjectRe: [patch] O(1) scheduler, -D1, 2.5.2-pre9, 2.4.17
On Wed, 9 Jan 2002, Ingo Molnar wrote:

>
> On Tue, 8 Jan 2002, Davide Libenzi wrote:
>
> > Mike can you try the patch listed below on custom pre-10 ?
> > I've got 30-70% better performances with the chat_s/c test.
>
> i've compared this patch of yours (which changes the way interactivity is
> detected and timeslices are distributed), to 2.5.2-pre10-vanilla on a
> 2-way 466 MHz Celeron box:
>
> davide-patch-2.5.2-pre10 running at default priority:
>
> # ./chat_s 127.0.0.1
> # ./chat_c 127.0.0.1 10 1000
>
> Average throughput : 123103 messages per second
> Average throughput : 105122 messages per second
> Average throughput : 112901 messages per second
>
> [ system is *unusable* interactively, during the whole test. ]
>
> davide-patch-2.5.2-pre10 running at nice level 19:
>
> # nice -n 19 ./chat_s 127.0.0.1
> # nice -n 19 ./chat_c 127.0.0.1 10 1000
>
> Average throughput : 109337 messages per second
> Average throughput : 122077 messages per second
> Average throughput : 105296 messages per second
>
> [ system is *unusable* interactively, despite renicing. ]
>
> 2.5.2-pre10-vanilla running the test at the default priority level:
>
> # ./chat_s 127.0.0.1
> # ./chat_c 127.0.0.1 10 1000
>
> Average throughput : 124676 messages per second
> Average throughput : 102244 messages per second
> Average throughput : 115841 messages per second
>
> [ system is unresponsive at the start of the test, but
> once the 2.5.2-pre10 load-estimator establishes which task is
> interactive and which one is not, the system becomes usable.
> Load can be felt and there are frequent delays in commands. ]
>
> 2.5.2-pre10-vanilla running at nice level 19:
>
> # nice -n 19 ./chat_s 127.0.0.1
> # nice -n 19 ./chat_c 127.0.0.1 10 1000
>
> Average throughput : 214626 messages per second
> Average throughput : 220876 messages per second
> Average throughput : 225529 messages per second
>
> [ system is usable from the beginning - nice levels are working as
> expected. Load can be felt while executing shell commands, but the
> system is usable. Load cannot be felt in truly interactive
> applications like editors.
>
> Summary of throughput results: 2.5.2-pre10-vanilla is equivalent
> throughput-wise in the test with your patched kernel, but the vanilla
> kernel is about 100% faster than your patched kernel when running reniced.
>
> but the interactivity observations are the real showstoppers in my
> opinion. With your patch applied the system became *unbearably* slow
> during the test.

Ingo, this is not the picture that i've got from my machine.
-------------------------------------------------------------------
AMD Athlon 1GHz 256 Mb RAM, swap_cnt patch :
# nice -n 19 chat_s 127.0.0.1 &
# nice -n 19 chat_c 127.0.0.1 20 1000

125236
123988
128048

with :

r b w swpd free buff cache si so bi bo in cs us sy
id
198 0 0 1476 28996 8024 89408 0 0 0 108 812 19424 12 87 1
216 0 1 1476 32388 8024 89412 0 0 0 0 523 56344 9 91 0
134 0 1 1476 32812 8024 89412 0 0 0 0 578 32374 9 91 0
96 1 1 1476 33540 8024 89412 0 0 0 0 114 7910 13 87 0
81 0 0 1476 35412 8024 89420 0 0 0 12 657 54034 12 88 0


pre-10 :

135684
127456
132420

the niced -20 vmstat has not been run for the whole test time and the
system seemed quite bad ( personal feeling, not for the whole test time
but for 1-2 sec spots ) compared with the previous test. The whole point
Ingo is that during the test we've had 200 tasks on the run queue with a
cs 8000..50000 !!?
AMD Athlon 1GHz, swap_cnt patch :

# chat_s 127.0.0.1 &
# chat_c 127.0.0.1 20 1000

118386
114464
117972


pre-10 :

90066
88234
92612

I was not able to identify any interactive feel difference here.
----------------------------------------------------------------------
Today i'll try the same on both my dual cpu system ( PIII 733 and PIII 1GHz )
I really fail to understand why you're asking everyone to run your test reniced ?!?



> - your patch in essence makes the scheduler ignore things like nice
> level +19. We *used to* ignore nice levels, but with the new load
> estimator this has changed, and personally i dont think i want to go
> back to the old behavior.

Ingo for the duration of the test the `nice -n 20 vmstat -n 1` never run
for about the 20 seconds.
With the swap_cnt correction it ran for 5-6 times.



> - the system i tested has a more than twice as slow CPU as yours. So i'd
> suggest for you to repeat those exact tests but increase the number of
> 'rooms' to something like 40 (i know you tried 20 rooms, i dont think
> it's enough), and increase the number of messages sent, from 1000 to
> 5000 or something like that.

Ingo, with 20 rooms my system was loaded with more than 200 tasks on the
run queue and was switching at 50000 times/sec.
Don't you think that it's enough for a single cpu system ??!!


> your patch indeed decreases the load estimation and interactivity
> detection overhead and code complexity - but as the above tests have
> shown, at the price of interactivity, and in some cases even at the price
> of throughput.

Ingo i tried to be the more impartial as possible and during the test i
was not able to identify any difference in system usability.
As i wrote you in private, the only spot i've had of system unusability
was running with stock pre10 ( but this could be happened occasionally ).




- Davide





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