Re: [Valgrind-users] Preliminary little speedup patch (seen 7% speedup)

[Nicholas N. <nj...@ca...>]

On Mon, 17 Mar 2003, Christian Leber wrote:

> I saw this realy big switch(opt){case 0x00....} statement and thought
> "this must be slow".
>
> So I tried the "Labels as Values" feature of the gcc.
> (http://www.dis.com/gnu/gcc/gcc_79.html#SEC79)
> Yes it is a gcc feature, but because is specially for x86/Linux I can't
> see a problem.

[snip]

> 13.54 -> 12.55
> that is a speedup of about 7% in this case
>
> If you (Julian or Nick) are perhaps interested in it, I would clean it up
> further and remove this one switch() { } statement.

Interesting.  Two comments:

1. Can you try it with a few other programs?  It would be nice to see if
the 7% speedup is consistent across programs.  Some programs I've used
for performance timing in the past:

   gzip
   bzip2
   latex
   konqueror (startup then quit immediately)

Batch programs are obviously more suitable for this.


2. The bottom of the webpage you mention says:

   "An alternate way to write the above example is

   static const int array[] = { &&foo - &&foo, &&bar - &&foo,
                                &&hack - &&foo };
   goto *(&&foo + array[i]);

   This is more friendly to code living in shared libraries, as it reduces
   the number of dynamic relocations that are needed, and by consequence,
   allows the data to be read-only."

Valgrind is packaged as a shared library.  Perhaps this might improve
things further?


If you could try these two experiments, and tell us the results, that
would be very helpful.

Thanks.

N