ARM - events lost and cmpxchg

Hi,

on ARM I noticed significant loss of events. At the
end of a trace I get
a printk message of over 100 lost events per second:

LTT : cpu_ : 122 events lost in cpu_ channel (cpu 0).

I have traced them to the place in ltt/ltt-relay.c
where the check
"*tsc == 0" is located. Is it normal that there are so
much events lost?
Which events are lost here?

To get it compile clean, I had to add the function
cmpxchg, which was
missing on arm, needed in ltt/ltt-relay.c. I don't
know, if it is
possible to avoid locking interrupts on arm:

static inline long cmpxchg(atomic_long_t *v, long old,
long new)
{
       long ret;
       unsigned long flags;

       raw_local_irq_save(flags);
       ret = v->counter;
       if (likely(ret == old))
               v->counter = new;
       raw_local_irq_restore(flags);

       return ret;
}

For this to work I also adapted the function
atomic_long_cmpxchg
in include/asm-generic/atomic.h. This will propably
break it for other
architectures, but I think "(l)->counter" should be
placed in the
architecture specific files.

 #define atomic_long_cmpxchg(l, old, new) \
-       ((long)cmpxchg(&((l)->counter), (old), (new)))
+       ((long)cmpxchg(l, (old), (new)))

Any suggestions?

Thanks,
Gunnar




	
		
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