RE: real world reverse debugging success story

[Marc Khouzam <marc.khouzam@ericsson.com>]

 

> -----Original Message-----
> From: Michael Snyder [mailto:msnyder@vmware.com] 
> Sent: November-11-09 8:08 PM
> To: Michael Snyder
> Cc: Marc Khouzam; gdb@sourceware.org
> Subject: Re: real world reverse debugging success story
> 
> Michael Snyder wrote:
> > Marc Khouzam wrote:
> >> [...]
> >>> Stats: used an 8 million instruction cache, running as a
> >>> ring buffer.  Had to record over 80 million instructions
> >>> before I tripped the bug.  Saved core file with record log
> >>> was 250 megabytes, and reloaded fine.
> >> Very impressive!
> >>
> >> How was the responsiveness?  I assume you didn't step
> >> over all those instuctions ;-)  So, you must have run the program
> >> and have it be recorded for a while.  I'm wondering if the 
> execution
> >> was annoyingly slow, or if it was ok.
> > 
> > The record phase was kind of slow, but I'm sure that was
> > impacted by a very large number of notifications to the effect
> > that process record would not record some memory because it
> > could not get the segment register.
> > 
> > Replay was not bad at all, about 15 seconds to get from
> > "goto-bookmark begin" to "goto-bookmark end".  For 80
> > million instructions, that's about 5 million insns / sec.

You know what, it just dawned on me that I never really payed
attention to the replaying spead :-O  I'm glad to hear it is good.

It is really the recording speed that I'm curious about.  I think
right now, this is a big limiting factor (understandably of course),
that would prevent the use of PRecord for real world applications.

I've had one person want to use PRecord to learn about a piece
of software.  They figured that they would record execution up to
a point in the code they know would hit, and then could go backwards
to find a more proper starting point for their investigation.  But
the recording was to slow to allow the application to reach far enough
fast enough.

I was happy to see that Hui had some ideas on how to improve the
recording speed.

This reverse 'thingy' as so much potential! :-)

> > 
> > Much faster than a first gen IBM PC, for instance!   ;-)
> 
> Oh, sorry, it was 8 million insns, so about 0.5M / sec.
> 
>