Re: [Xenomai-help] Slow hard drive access in xenomai

[Jan Kiszka <jan.kiszka@domain.hid>]

Am 25.10.2010 12:47, Gilles Chanteperdrix wrote:
> Eric Noulard wrote:
>> 2010/10/24 Peter Pastor <peter.pastor@domain.hid>:
>>> Hey Gilles,
>>> I am in the process to configure the xenomai kernel as you suggested.
>>> I found and disabled the options that you suggested (NUMA, SPARSEMEM,
>>> SECCOMP, AUDITSYSCALL, KPROBES, FTRACE, SELINUX), However, I could not
>>> disable SPARSEMEM. Searching for SPARSEMEM in the kernel configuration
>>> simply says "Symbol: SPARSEMEM [=y]" and does not give me any further info.
>>> Can you tell me how to disable it ?
>>
>> SPARSEMEM may be a dependence for other options.
>> If you look into the mm/Kconfig file
>> http://lxr.linux.no/#linux+v2.6.32/mm/Kconfig#L103
>> you may discover which options you have may need SPARSEMEM.
>>
>> For example the CONFIG_MEMORY_HOTPLUG depends on SPARSEMEM.
>>
>>> Also, I disabled NUMA even though the info states "For 64-bit this is
>>> recommended if the system is Intel Core i7 (or later), AMD Opteron, or
>>> EM64T" and my system is a 64bit, with 8 Intel Xeon cores. Hope that is ok...
>>
>> NUMA stands for Non Uniform Memory Access essentially it is for multiprocessor
>> machine which have a memory layout which is not "symmetric" (aka Uniform) with
>> respect to each processor.
>> You have some "pictured" example of NUMA systems on the HWLOC project
>> http://www.open-mpi.org/projects/hwloc/
>> http://www.open-mpi.org/projects/hwloc/doc/v1.0.2/#examples
>>
>> Now I really don't know if enabling NUMA handling is mandatory for NUMA systems
>> I guess yuo could disable NUMA handling at kernel level but yuo may
>> get performance
>> weirdness because the kernel is not aware of the NUMA nature.
>>
>> This is pure guess, I let others give you a more "secure" answer to this.
> 
> From what I understood NUMA means that you have several "nodes" with a
> fast local memory and a slow remote memory. If you only have one CPU,
> which accesses only one DRAM bank, you do not need NUMA. In any case,
> the boot logs will tell you how many NUMA nodes are created. But since
> Peter never sent a full boot log, I have no idea what the boot logs say.
> 

NUMA should not cause such issues (we are running Xenomai on real NUMA),
nor should it cause noticeable slowdowns when enabled but unused.

Let's focus on the core issue, a potentially spurious IRQ: Peter, can
you check if 2.6.35 shows the same symptoms (2.6.31 is unmaintained anyway)?

Jan

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