Wireshark-dev: Re: [Wireshark-dev] The cost of memory allocation
From: Graham Bloice <[email protected]>
Date: Wed, 21 Sep 2016 09:49:15 +0100

On 21 September 2016 at 09:29, Paul Offord <[email protected]> wrote:

I’m not happy with the performance of the transum dissector and so I’ve started some analysis.  I’ve never used VS performance profiling before but I plan try to investigate this problem using it.  In the meantime I’ve used a tool that I’m reasonably familiar with called PerfView.  It’s produced some interesting results which I thought I’d share.


The problem I’m having is that with transum enabled load time for a 50MB file increases from 5 seconds to 10 seconds, but then subsequent loads of the same file go out to about 40 or 50 seconds.



Above (or attached depending on your email system) is a screen shot showing the time spent in various functions when a load of the file took 44.8 seconds.  At the top of the image is a transum function called decode_gtcp.  The image shows that 50.7% of the total load time was spent executing in this function.  Then we see all of the nested functions with the proportion of time spent in each of those.


What I notice is that a lot of time is being spent in glib functions, and in particular the time is being spent allocating and freeing memory.



Using a slightly different view we can see that across the whole of the process during a load file with transum enabled more than 66% of the time is spent messing around with memory.


I haven’t yet figured out why I get inconsistent load times, and I don’t know what I can do about any of the above, but I thought it might be of general interest.


Best regards…Paul

Release or debug build?

Graham Bloice