Wireshark · Wireshark-dev: Re: [Wireshark-dev] [Wireshark-commits] rev 35393: /trunk/epan/dissectors/ /trunk/epan/dissectors/:

[Jeff Morriss <jeff.morriss.ws@xxxxxxxxx>]

Martin Mathieson wrote:
>     After remembering that profiling (at least in its easiest form with
>     the 'time' command) isn't so hard, I played around a bit. After
>     building a decent-sized dct2000 file (taking the sample from
>     SampleCaptures and merging it with itself until I had a 276 Mb
>     file), I tried before and after this change and I can't find a
>     measurable difference in the CPU usage.  I even tried forcing my
>     (AMD) CPU down to 1 GHz to exaggerate the difference, but I still
>     got only a couple of seconds CPU time difference out of over 5
>     minutes--and in that case rev 35393's code was faster.
>
>     Maybe I'll try tomorrow on a SPARC: I know that memcpy()s are a lot
>     more expensive there than on x86.
>
>
> I think you win, the difference isn't worth it and it'd be better not to 
> leave unnecessary examples of tvb_get_ptr() use around.

I tried with SPARC today and I do see a consistent 0.9% difference in 
CPU time before and after 35393.  (In particular I see about 6-7 seconds 
of extra CPU time in a tshark job that takes around 11 minutes and 50 
seconds.)

Don't know if that difference is significant enough to matter.

> Soon after that I realised that to spend 30% of CPU reading text lines 
> from the file (in wiretap) was too high.  When I configured to compile 
> without zlib support that went down to 0.3%, and I haven't worried too 
> much about performance since then.

I remember you mentioning that before...  Another reason to kick zlib 
out so we can be sure to have fast random access to files. :-)