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authorEmil Medve <Emilian.Medve@Freescale.com>2007-11-14 03:24:04 +1100
committerPaul Mackerras <paulus@samba.org>2007-12-21 15:05:58 +1100
commiteda09fbdcd8c5afaa81c2f1d28e8b9725bad4d5a (patch)
tree0afe6e81172fc9508f8e4c13598a276fe3d043c6 /Documentation/ia64
parent1fe58a875e4bb08125c657b1b91ac515d2bdbcbe (diff)
[POWERPC] Optimize counting distinct entries in the relocation sections
When a module has relocation sections with tens of thousands of entries, counting the distinct/unique entries only (i.e. no duplicates) at load time can take tens of seconds and up to minutes. The sore point is the count_relocs() function which is called as part of the architecture specific module loading processing path: -> load_module() generic -> module_frob_arch_sections() arch specific -> get_plt_size() 32-bit -> get_stubs_size() 64-bit -> count_relocs() Here count_relocs is being called to find out how many distinct targets of R_PPC_REL24 relocations there are, since each distinct target needs a PLT entry or a stub created for it. The previous counting algorithm has O(n^2) complexity. Basically two solutions were proposed on the e-mail list: a hash based approach and a sort based approach. The hash based approach is the fastest (O(n)) but the has it needs additional memory and for certain corner cases it could take lots of memory due to the degeneration of the hash. One such proposal was submitted here: http://ozlabs.org/pipermail/linuxppc-dev/2007-June/037641.html The sort based approach is slower (O(n * log n + n)) but if the sorting is done "in place" it doesn't need additional memory. This has O(n + n * log n) complexity with no additional memory requirements. This commit implements the in-place sort option. Signed-off-by: Emil Medve <Emilian.Medve@Freescale.com> Signed-off-by: Paul Mackerras <paulus@samba.org>
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