Re: [PATCH] Linux Kernel Markers 0.13 for 2.6.17

[Mathieu Desnoyers]

* Jeremy Fitzhardinge (jeremy@xxxxxxxx) wrote:
> Mathieu Desnoyers wrote:
> >Just as a precision :
> >
> >The following sequence (please refer to the code below for local symbols
> >1 and 2) :
> >
> >1:
> >preempt_disable()
> >call (*__mark_call_##name)(format, ## args);
> >preempt_enable_no_resched()
> >2:
> >
> >is insured because :
> >
> >1 is part of an inline assembly with rw dependency on __marker_sequencer
> >the call is surrounded by memory barriers.
> >2 is part of an inline assembly with rw dependency on __marker_sequencer
> >  
> 
> What do you mean the call is surrounded by memory barriers?  Do you mean 
> a call has an implicit barrier, or something else?
> 
Yes, preempt_disable() has a barrier(), on gcc :
__asm__ __volatile__("": : :"memory").


> Either way, this doesn't prevent some otherwise unrelated 
> non-memory-using code from being scheduled in there, which would not be 
> executed.  The gcc manual really strongly discourages jumping between 
> inline asms, because they have basically unpredictable results.
> 

Ok, I will do the call in assembly then.

Mathieu


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