[ltt-dev] Bug in LTTv statistics ?
compudj at krystal.dyndns.org
Fri Jul 16 10:54:02 EDT 2010
* François Godin (copelnug at gmail.com) wrote:
> Thank for the answer. That made it clear but it bring others questions :
> Is the state for the "page_fault_entry" event is the previous state of the
> cpu ? I suppose but a confirmation would be welcome.
Well, in reality, the page fault entry event is recorded in page fault
context. So the textdump has it right. But that's really just a
"modeling artefact" to have one or the other.
> I try to understand why on one trace, is there still "page_fault_entry" in
> TRAP mode. I checked the previous correction, and while it find the right
> states for all events except those that LTTv put in "TRAP" mode. Am I
> missing something else or is it a glitch in LTTv?
No sure what you mean. Can you try to explain a little more ?
> 2010/7/15 Mathieu Desnoyers <compudj at krystal.dyndns.org>
> > * François Godin (copelnug at gmail.com) wrote:
> > > I think I've found another bug in the LTTv statistics. The problem is
> > with
> > > page_fault_entry event. In the textdump they are classified as being in
> > mode
> > > TRAP but they appear in SYSCALL and USER_MODE mode in the statistics
> > view.
> > This comes from the way callbacks are dealt with in the priority hook
> > list:
> > When an event is encountered, the statistics "before" event callbacks
> > are called first, then the state "before" event callbacks are called,
> > then the event callbacks per se (e.g. textdump) are called, and then the
> > after state, followed by after stats hooks.
> > So given that the statistics hooks are called before the state
> > modification, and that the textdump hooks are called after the state
> > modification, there is a discrepancy between the two. But in reality,
> > the statistic hook has the correct state associated (the trap occurs its
> > calling context, not in "itself"). But how to fix the textdump is
> > unclear to me.
> > Thanks,
> > Mathieu
> > --
> > Mathieu Desnoyers
> > Operating System Efficiency R&D Consultant
> > EfficiOS Inc.
> > http://www.efficios.com
> François Godin
Operating System Efficiency R&D Consultant
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