linux-kernel - Re: [ANNOUNCE/RFC] Really Fair Scheduler

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Date:	Fri, 31 Aug 2007 11:36:55 +0200
From:	Mike Galbraith <efault@....de>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, peterz@...radead.org
Subject: Re: [ANNOUNCE/RFC] Really Fair Scheduler

On Fri, 2007-08-31 at 04:05 +0200, Roman Zippel wrote:
> Hi,

Greetings,

> I'm glad to announce a working prototype of the basic algorithm I
> already suggested last time.

(finding it difficult to resist the urge to go shopping, I
fast-forwarded to test drive... grep shopping arch/i386/kernel/tcs.c if
you're curious;)

I plunked it into 2.6.23-rc4 to see how it reacts to various sleeper
loads, and hit some starvation.  If I got it in right (think so) there's
a bug lurking somewhere.  taskset -c 1 fairtest2 resulted in the below.
It starts up running both tasks at about 60/40 for hog/sleeper, then
after a short while goes nuts.  The hog component eats 100% cpu and
starves the sleeper (and events, forever).

runnable tasks:
            task   PID        tree-key         delta       waiting  switches  prio        sum-exec        sum-wait       sum-sleep    wait-overrun   wait-underrun
------------------------------------------------------------------------------------------------------------------------------------------------------------------
        events/1     8  13979193020350 -3984516524180  541606276813      2014   115               0               0               0               0               0
R      fairtest2  7984  10027571241955 -7942765479096 5707836335486       294   120               0               0               0               0               0
       fairtest2  7989  13539381091732 -4424328443109 8147144513458       286   120               0               0               0               0               0

taskset -c 1 massive_intr 3 9999 produces much saner looking numbers,
and is fair...

runnable tasks:
            task   PID        tree-key         delta       waiting  switches  prio        sum-exec        sum-wait       sum-sleep    wait-overrun   wait-underrun
------------------------------------------------------------------------------------------------------------------------------------------------------------------
    massive_intr 12808  29762662234003         21699       -506538      4650   120               0               0               0               0               0
R   massive_intr 12809  29762662225939          -687         53406      4633   120               0               0               0               0               0
    massive_intr 12810  29762662220183          7879        453097      4619   120               0               0               0               0               0


View attachment "fairtest2.c" of type "text/x-csrc" (3950 bytes)