[ltt-dev] LTTng with 2.6.22.18 and lost events

[Mathieu Desnoyers]

* Akyurek, Ali (EXT) (ali.akyurek.ext at siemens.com) wrote:
> Hi all,
>  
> I've solved the problem with the gui.
>  
> Problem is that i'm running the deamon seperate than lttctl, then i
> couldn't see facilites message.
> After adding -d parameter, i got the facility messages, then i'm able to
> see the results with lttv.
>  
> But i'm still thinking how to solve lost events problem.
> 

This ARM implementation uses a special version of the read seqlock in
the ARM tracing time source. You might want to audit
include/asm-arm/ltt.h to see if increasing the max loop value (which was
5 I think) helps. Basically, it fails after 5 loops so we don't create
an infinite loop if we are nested over the write seqlock.

Also, another possibility : I remember that some version had a problem
with this lock because the update_timer event was located within the
write seqlock of the timer irq handler. It's been fixed in the following
versions, so you might want to audit this too, because then all
update_timer events gets lost.

Mathieu


> 
> ________________________________
> 
> Von: Akyurek, Ali (EXT) 
> Gesendet: Donnerstag, 22. Januar 2009 16:40
> An: ltt-dev at lists.casi.polymtl.ca
> Betreff: [ltt-dev] LTTng with 2.6.22.18 and lost events
> 
> 
> Hi all,
>  
> I'm trying LTTng with a 2.6.22.18 kernel on an Arm machine. I've applied
> patch-2.6.22-rc4-mm2-lttng-0.9.10 patched with some corrections.
> Everything went well, until destroying the channels. 
>  
> I get the following message: 
>  
> "LTT : cpu : 6769 events lost in cpu channel (cpu 0)."
>  
> So when i try to open with lttv-gui, it doesn't work.
>  
> I've searched but found nothing except Mathieu, saying that it may be
> related to buffer size or timestamp.
>  
> Is there anyone having an idea?
> Thanks.
>  
> Mit freundlichem Gruss / Best Regards
> Ali
>  

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-- 
Mathieu Desnoyers
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