[Crash-utility] [PATCH v5 0/6] Improve kernel modules symbol searching performance

[Tao Liu]

Hi Kazu,

On Fri, Oct 15, 2021 at 10:12 AM HAGIO KAZUHITO(萩尾　一仁)
<k-hagio-ab at nec.com> wrote:
>
> Hi Tao Liu,
>
> One more comment, the mod_syment_hash also should be printed by help -s,
> like symname_hash.
>
> crash> set debug 1
> debug: 1
> crash> help -s
> ...
> val_hash_iterations: 530  (avg: 75.7)
>    symname_hash[512]: ff7808
>     [  0]:  57  [  1]: 121  [  2]:  28  [  3]:  79  [  4]: 165  [  5]:  51
>     [  6]:  57  [  7]:  99  [  8]:  61  [  9]:  98  [ 10]: 108  [ 11]:  68
>

Thanks for pointing this out. I will implement code for it.

> The other patches (2 to 6) look good to me.
>

Thanks for reviewing the patch, I will get it improved for the v6 patch.

Thanks,
Tao Liu

> Thanks,
> Kazu
>
>
> -----Original Message-----
> > Currently the sequence for symbol_search to search a symbol is: 1) kernel
> > symname hash table, 2) iterate all kernel symbols, 3) iterate all kernel
> > modules and their symbols. In the worst case, if a non-exist symbol been
> > searched, all 3 stages will be went through. The time consuming status for
> > each stage is like:
> >
> >     stage 1         stage 2         stage 3
> >     0.007000(ms)    0.593000(ms)    2.421000(ms)
> >
> > stage 3 takes too much time when comparing to stage 1. This patch introduces
> > a symname hash table for kernel modules, to improve the performance of symbol
> > searching.
> >
> > Functions symbol_search and symbol_exists are fundamental and widely used by
> > other crash functions, thus the benefit of performance improvement can
> > get accumulated. For example, "ps -m" and "irq" commands, which call
> > the functions many times, will become faster with the patch.
> >
> > v4 -> v5:
> >
> > 1) Seperated kernel modules syment install from kernel syment install,
> > making them 2 independent functions. Thus kernel modules syment can get sorted
> > when installed into mod_syment_hash. And spn->cnt stays untouched in v5.
> > 2) Removed syment_is_installed check, it is no longer needed for the new
> > kernel modules syment install function.
> > 3) Splitted the patches into smaller ones for better patch review.
> > 4) Changed SYMNAME_HASH_INDEX macro into symname_hash_index function.
> > 5) v5 patch can be applied to master branch, for crash-7-branch it needs
> > slightly modification.
> >
> > Tao Liu (6):
> >   Implement install and remove operations for mod_symname_hash
> >   Integrate symbol_search with mod_symname_hash search
> >   Extend symname_hash_search with hash table select
> >   Intergrate symbol_exists with mod_symname_hash search
> >   Sync module symbols into mod_symtable whenever module symbols change
> >   Refactor SYMNAME_HASH_INDEX macro to be a function
> >
> >  defs.h    |   3 +-
> >  kernel.c  |   1 +
> >  symbols.c | 212 ++++++++++++++++++++++++++++++++++--------------------
> >  3 files changed, 137 insertions(+), 79 deletions(-)
> >
> > --
> > 2.29.2
>