[PATCH] Improve performance of strcat

[Wilco Dijkstra]

> Carlos O'Donell wrote:
> On 08/07/2014 09:27 AM, Wilco Dijkstra wrote:
> > Hi,
> >
> > This patch improves strcat performance by using strlen and strcpy. Strlen has a fast C
> > implementation, so this improves performance even on targets which don't have an optimized
> strlen
> > and strcpy - it is 25% faster in bench-strcat. On targets which don't provide an optimized
> strcat
> > but which do have an optimized strlen and strcpy, performance gain is > 2x.
> 
> What benchmarks did you use to test this performance gain?
> 
> Did you use glibc's microbenchmark?
> 
> What numbers did you get?

These results are for the GLIBC benchtests/bench-strcat.c - I increased the iterations
significantly and profiled the results with a high tickrate to verify the timings.

 65.74%       11343  bench-strcat  bench-strcat       [.] simple_strcat
 24.90%        4307  bench-strcat  libc-2.20.90.so    [.] strcpy
  5.20%         902  bench-strcat  libc-2.20.90.so    [.] strlen
  1.22%         214  bench-strcat  bench-strcat       [.] do_test
  1.08%         190  bench-strcat  libc-2.20.90.so    [.] strcat

So strcat+strlen+strcpy=31.18% vs simple_strcat 65.74%, ie. 2.1x speedup.

Wilco