Gilles Chanteperdrix <[email protected]> wrote on
08/29/2011 12:13:48 AM:
> On 08/26/2011 11:49 PM, George Broz wrote:
> >> Gilles Chanteperdrix <[email protected]> wrote on
> > 08/26/2011 02:18:05 PM:
> >> On 08/26/2011 10:42 PM, George Broz wrote:
> >>> Hello,
> >>>
> >>> I'm experiencing very large overruns in the neighborhood of 10 to 50
> >>> *milli-seconds* as reported by the Xenomai latency tool in user-task
> > mode
> >>> whenever the Linux OS is heavily loaded. Under lighter loads these
are
> > in
> >>> the 30 to 70 micro-second (normal) range.
> >>>
> >>> My system is:
> >>> - Linux 2.6.37.6 (32-bit), Ubuntu 10.10 distribution
> >>> - Xenomai 2.5.6 using I-pipe patch adeos-ipipe-2.6.37.6-x86-2.9-02
> >>> - Intel x86 Atom (dual-core) CPU D510 @ 1.66GHz
> >>> - Emb. dev board from Intel (ICH8M ctrlr, Ethernet h/w for e1000e)
> >>> - Xenomai configured w&w/o --enable-smp --enable-x86-tsc options
> >>> - gcc version 4.4.5
> >>>
> >>> I've followed all of the recommendations for kernel configuration
and
> > have
> >>> disabled CPU sleep features in the BIOS such as SpeedStep and
> > C-States.
> >>> Legacy USB has been disabled in the BIOS. Hyperthreading has also
been
> >
> >>> disabled, although I don't think it matters.
> >>
> >> Have you tried to enable the SMI workaround?
> >>
> >> --
> >> Gilles.
> >>
> >
> > Yes - SMI workaround was enabled when the overruns were observed.
>
> Could you try disabling CONFIG_SMP to see if you get the same behaviour,
> and take a few traces?
> If you processor supports 64 bits mode, could you try running a 64 bits
> kernel?
>
>
> --
> Gilles.
>
I disabled CONFIG_SMP and did not get the same behaviour - latencies were
normal (albeit now slightly increased). The processor supports 64 bit
mode, but my initial attempt to get that working failed (for unrelated
reasons).
I then started looking at the hardware some more after Jan's comment, and
found another CPU frequency throttling mechanism that exists in the Atom
N450 and D510. This is the "thermal monitor" (TM1) as described in this
Intel document:
http://download.intel.com/embedded/processors/thermalguide/323439.pdf
Even though my dev. board had a fan, adding even more cooling
significantly reduced the occurrence of the overruns (but they would still
occur occasionally). I then disabled the thermal monitor (TM1) feature
from the BIOS, and since then have not seen any more happen (after about 2
hours of testing). I will test more tomorrow, and post if I see the
problem still exists.
Thanks very much for your (and Jan's) help.
--George
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