[Bug dynamic-link/15310] _dl_sort_fini is O(n^3) causing slow exit when many dsos

["adhemerval.zanella at linaro dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=15310

Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |adhemerval.zanella at linaro dot o
                   |                            |rg
         Resolution|---                         |FIXED

--- Comment #27 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
The testcase which creates a linear chain test to demostrate the O(n^3)
behavior shows an improvement with the new DSO sorting algorithm from
15a0c5730d1d5ae:

$ time ./testrun.sh /tmp/test/main1000 2>&1 >/dev/null 

real    0m1.641s
user    0m1.565s
sys     0m0.076s

$ time GLIBC_TUNABLES=glibc.rtld.dynamic_sort=2 ./testrun.sh /tmp/test/main1000
2>&1 >/dev/null 

real    0m0.316s
user    0m0.219s
sys     0m0.095s

And profile shows similar improvement:

$ perf record ./testrun.sh /tmp/test/main1000
[...]
$ perf report --stdio -q
[...]
    78.28%  ld-linux-x86-64  ld.so             [.] _dl_sort_maps
     6.77%  ld-linux-x86-64  ld.so             [.] do_lookup_x
     5.03%  ld-linux-x86-64  ld.so             [.] memmove
     2.64%  ld-linux-x86-64  ld.so             [.] strcmp

$ perf record env GLIBC_TUNABLES=glibc.rtld.dynamic_sort=2 ./testrun.sh
/tmp/test/main1000
[...]
$ perf report --stdio -q --dso=ld.so
[...]
    41.44%  ld-linux-x86-64  [.] do_lookup_x
    13.76%  ld-linux-x86-64  [.] strcmp
     6.01%  ld-linux-x86-64  [.] _dl_map_object
     5.17%  ld-linux-x86-64  [.] _dl_name_match_p
     1.34%  ld-linux-x86-64  [.] _dl_map_object_from_fd
     0.69%  ld-linux-x86-64  [.] _dl_add_to_namespace_list

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