Re: [PATCH v2] dwarf_loader: use a better hashing function

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Feb 12, 2021 at 09:37:22AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Feb 12, 2021 at 12:01:04AM -0800, Bill Wendling escreveu:
> > This hashing function[1] produces better hash table bucket
> > distributions. The original hashing function always produced zeros in
> > the three least significant bits. The new hashing function gives a
> > modest performance boost:
> 
> Some tidbits:
> 
> You forgot to CC Andrii and also to add this, which I'm doing now:
> 
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> 
> :-)

See below the full cset, that will go public after some more tests here.

- Arnaldo

commit 9fecc77ed82d429fd3fe49ba275465813228e617 (HEAD -> master)
Author: Bill Wendling <morbo@google.com>
Date:   Fri Feb 12 00:01:04 2021 -0800

    dwarf_loader: Use a better hashing function, from libbpf
    
    This hashing function[1] produces better hash table bucket
    distributions. The original hashing function always produced zeros in
    the three least significant bits. The new hashing function gives a
    modest performance boost:
    
      Original: 0:11.373s
      New:      0:11.110s
    
    for a performance improvement of ~2%.
    
    [1] From the hash function used in libbpf.
    
    Committer notes:
    
    Bill found the suboptimality of the hash function being used, Andrii
    suggested using the libbpf one, which ended up being better.
    
    Signed-off-by: Bill Wendling <morbo@google.com>
    Suggested-by: Andrii Nakryiko <andrii@kernel.org>
    Cc: bpf@vger.kernel.org
    Cc: dwarves@vger.kernel.org
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>