Re: Tracing memcpy for MIPS

Hrm,

Thinking a little more about your problem, I come with a few other
things to consider:

ltt/ltt-serialize.c uses memcpy() for strings, arrays, and sequences.
You must make sure you do not use any %s, %v or %a in your marker format
string within memcpy, or you will end up with an infinite recursion.

Second thing: 
you will find memcpy implementation in arch/mips/lib/memcpy.S and
memcpy-inatomic.S.

My suggestion, to keep it simple, is that you rename the original
memcpy into memcpy_notrace, then create a wrapper memcpy inline function
in asm-mips/string.h which would look like:

extern void *memcpy_notrace(void *__to, __const__ void *__from, size_t __n);

static inline void *memcpy(void *__to, __const__ void *__from, size_t __n)
{
  __label__ memcpy_label;
  trace_mark(lib_memcpy, "%lu", &&memcpy_label);
memcpy_label:
  return memcpy_notrace(__to, __from, __n);
}


The second alternative is (it adds a function call):

In asm-mips/string.h:

extern void *memcpy_notrace(void *__to, __const__ void *__from, size_t __n);
extern void *memcpy(void *__to, __const__ void *__from, size_t __n);

And create arch/mips/lib/memcpy.c:

void *memcpy(void *__to, __const__ void *__from, size_t __n)
{
  trace_mark(lib_memcpy, "%lu", __builtin_return_address(0));
  return memcpy_notrace(__to, __from, __n);
}

You should probably do the same for memcpy inatomic.

Mathieu


* Sagar Borikar ([email protected]) wrote:
>   
> Hello,
> 
> I am consistently using LTTng for tracing the MIPS system. While adding the events, I was bit stuck in finding out which of the kernel memcpy function is consuming lot of CPU. I need to search a kernel call which is having highest probability of stalling the cpu. So in short, I would like to see backtrace in LTTng. Can anyone point me out about using backtracking feature in LTTng if at all it is present?
> 
> Thanks in advance,
> 
> Sagar
> 

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-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
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