debug nic_drv

[Keqin Sun]

Hi Norman,
     Thank you for the information. This optimization seems very important, I'm
willing to follow your work. But I'm afraid I do not fully understand how the
entire system working. Where can I get some detailed documentations about how
does gdb_monitor work and how does fiasco.OC or Genode map memory for each app?
I have been read several docs on the Genode website but still puzzled.

Regards
keqin

On 星期二, 四月 23, 2013 5:47 pm, Norman Feske wrote:
-----------------------------------------------------------------------------------

-----------------------------------------------------------------------------------
Hi Keqin,

>      You are right. It works. But sometimes it is slow, I guess there also has some
> information mess up the GDB protocal. Thank you very much.

congratulations that you got it working!

Regarding the slowness, I can partially explain the current state. The
main reason lies in the way how GDB monitor peeks and pokes in the
target's address space. For each individual memory access, we traverse
the target's memory-mapping structures, locally map the corresponding
memory into the GDB monitor's address space, perform the access, and
revert the mapping. When doing a debug operation such as a backtrace or
memory dump, this sequence is performed over and over again.
Consequently a lot of superfluous (and costly) map and unmap operations
are performed. Obviously, there is the opportunity to optimize those
memory accesses by the means of caching. I actually started to implement
this optimization via a so-called 'Memory_model' in GDB monitor:


https://github.com/genodelabs/genode/blob/master/ports/src/app/gdb_monitor/gdbserver/genode-low.cc

However, the implementation is not complete, yet. I.e., the cache gets
not flushed when needed, which leads to coherency problems. For this
reason, I have set NUM_MAPPED_REGIONS to just 1, effectively disabling
the optimization. If you like to pick up the work where I left, you are
more than welcome to increase the value and try to fix the remaining
inconsistency issues. ;-)

Cheers
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

http://www.genode-labs.com ・ http://genode.org

Genode Labs GmbH ・ Amtsgericht Dresden ・ HRB 28424 ・ Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth

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