On Mon, 2007-04-09 at 11:20 +0200, Dmitry Adamushko wrote:
> On 09/04/07, Mike Galbraith <[email protected]> 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).
Yeah, 23.7% idle. Hrm.
> 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.
Yeah. There's a patch floating around that is supposed to fix some of
the error. I'm going to test with it, and I'm rummaging around a bit as
well. I know for sure that frequency scaling will screw up the test
proggy's calibration here, but I test with it locked to max, and in any
case the hog half should eat any cpu not being used by the tenp half.
-Mike
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