linux-kernel - Re: SD scheduler testing hitch

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Date:	Mon, 9 Apr 2007 11:20:16 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Mike Galbraith" <efault@....de>
Cc:	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: SD scheduler testing hitch

On 09/04/07, Mike Galbraith <efault@....de> wrote:
> On Sun, 2007-04-08 at 21:34 +0300, Al Boldi wrote:
> > Mike Galbraith wrote:
> > > On Sat, 2007-04-07 at 19:17 +0200, Mike Galbraith wrote:
> > > > I lowered the time to 500us, and ran at nice -10.. it starves tenpercent
> > > > here every time.  (ran as taskset -c 1 nice -n -10 ./fairtest)  The
> > > > starving 10% duty cycle task has trouble getting 1% CPU.
> > >
> > > Hmm.  Playing with it some more today, it still happens, but it's not
> > > very repeatable.  Something is odd.  I wonder if any SD using readers
> > > will try it.
> >
> > Tried it on mainline 2.6.20.3.
> > It's not easily repeatable, but it's got the same problem.

In my case, it's easily reproducible. Below is a mainline 2.6.19.

Look at both %CPU and TIME+ (sched_time).

top - 10:55:00 up 33 min,  8 users,  load average: 1.07, 0.61, 0.51
Tasks:  76 total,   2 running,  74 sleeping,   0 stopped,   0 zombie
Cpu(s): 76.0% us,  0.3% sy,  0.0% ni, 23.7% id,  0.0% wa,  0.0% hi,  0.0% si
Mem:    256592k total,   251888k used,     4704k free,    46516k buffers
Swap:   272120k total,     4924k used,   267196k free,    90048k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 8113 dimm      15   0  1460  436  360 R 74.4  0.2   1:43.63 fairtest_xx
 8114 dimm      15   0  1460  108   32 S  0.3  0.0   0:00.15 fairtest_xx


If you take a look at my previous report, you'll also notice
"strangeness" with both cpu% and sched_time.

sched_clock() is based on "tsc" and it's available for my CPU. So
maybe something fishy is going on with accounting.

I just wonder, why it's so easily reproducible in my case for both
mainline and SD (besides a 2.6.13 mainline, but I have to re-run all
the tests letting tenp run longer for the "sched_time" to be
accumulated)...

-- 
Best regards,
Dmitry Adamushko
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