[ltt-dev] smp_call_function_single not implemented

Mathieu Desnoyers compudj at krystal.dyndns.org
Mon Jul 27 09:58:41 EDT 2009

* Ajit R (ajitrzid at yahoo.com) wrote:


> Hello
>    I am trying to include LTT support on an ARM11 MPCORE (ARMv6) based
>    target, which runs uclinux 2.6.23 and runs SMP + CPU HOTPLUG with 2
>    cores. I have been able to patch the LTT sources ( on this
>    kernel source tree. Compilation fails with an error
>    "smp_call_function_single: undefined reference". There is no
>    implementation of this function found in the source. Is there a way
>    I can get the same functionality by other means?

I think you may have to port a more recent smp IPI implementation to
your older kernel. Anyway have a look at linux/smp.h and kernel/smp.c to
try to figure out what you have.

>    This implementation of LTT is based on timer interrupts. Is it
>    possible to backport the 2.6.29 based OMAP V7 implementation (as it
>    uses the PMC + the CCNT and which the MPCORE too has) or do you
>    foresee any issues (dependencies/etc) ?

The current OMAPv7 PMC+CCNT implementation will need to be made
multi-core aware. Currently, the CCNT registers of the multiple cores
are not synchronized with each other (we would need to use the
kernel/time/tsc-sync.c code to synchronize these clocks when the trace
clock is about to be used and at return from idle/power save mode.

We also need to make sure return from idle states won't interfere with
cycle counter correctness of other CPUs. BTW, if someone would like to
send me an engineering sample of a recent ARM MPCORE, it may become
useful in a very near future.


> Ajit
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Mathieu Desnoyers
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