Re: [PATCH] reduce the time of finding symbols for module

[zhouchengming]

On 2017/3/28 17:00, Miroslav Benes wrote:
> Hi,
>
> On Tue, 28 Mar 2017, Zhou Chengming wrote:
>
> > It's reported that the time of insmoding a klp.ko for one of our
> > out-tree modules is too long.
> >
> > ~ time sudo insmod klp.ko
> > real	0m23.799s
> > user	0m0.036s
> > sys	0m21.256s
>
> Is this stable through several (>=10) runs? 23 seconds are really
> suspicious. Yes, there is a linear search through all the kallsyms in
> kallsyms_on_each_symbol(), but there are something like 70k symbols on my
> machine (that is, way less than 1M). 23 seconds are somewhat unexpected.

Yes, it's stable through several runs.

I think the big reason is that our out-tree module used a lot of static local
variables. We can see '.rela.kpatch.dynrelas' contains many entries, so it will
waste a lot of time if we use kallsyms_on_each_symbol() to find these symbols of module.

Relocation section '.rela.kpatch.funcs' at offset 0x382e0 contains 3 entries:
  Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000000000  003300000101 R_AARCH64_ABS64   0000000000000000 value_show + 0
000000000020  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 8
000000000028  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 0

Relocation section '.rela.kpatch.dynrelas' at offset 0x38328 contains 2562 entries:
  Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000000000  003300000101 R_AARCH64_ABS64   0000000000000000 value_show + 14
000000000018  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 13
000000000020  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 0
000000000040  003300000101 R_AARCH64_ABS64   0000000000000000 value_show + 20
000000000058  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 13
000000000060  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 0

> If it is a problem, can we fix kallsyms_on_each_symbol() and replace the
> linear search with something better? All users would benefit...

Yes, it's better if we can improve the linear search, but I can't think of that...

Thanks.

> Thanks,
> Miroslav
>
> .