[Crash-utility] [PATCH v2] Improve the performance of symbol searching for kernel modules

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> > (BTW, at a glance I'm not sure why the 2nd stage is needed...
> > sp_hashed was already checked with STREQ in symname_hash_search if found,
> > otherwise st->synmane_hash should include all kernel symbols..)
> >
> Hello Kazu,
> 
> Yes, from my view I also think the 2nd stage is not necessary, I have
> thought about removing
> it as well, but I just don't want to go too far at one step. :-)

OK, I see.

> > One more, do you have any slow command that will be especially improved
> > by the patch?  I'm ok with the sym command taking 3ms :-)
> > I'd like to know why the patch should be applied or how much the worst
> > command etc. will be improved, to see the importance of it.
> >
> 
> No, I don't have a specific slow command. Because the modified functions
> symbol_search and symbol_exists are fundamental and widely used by
> other crash functions, thus the benefit of performance improvement can
> get accumulated. In addition, the time consumption for T3 shortened greatly,
> from 2.4 to 0.017, maybe this can be one of the reasons.

OK.

As far as I've checked a large machine (with 192 CPUs), there are not many
commands but several commands call symbol_search and symbol_exists returning
"not found" many times:

      symbol_search  symbol_exists
       found  NULL    found  NULL
startup   95    21       29    21
ps -m   1951  1951        0     0
irq     1850     0        0 13448
irq -a  1850     0      884 10777
irq -s  1850     0      884 10777
timer    193   193        0     0

Actually, these commands were obviously improved by the patch.
So let's add some explanation like this to the commit log:

" 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."

Anyway, I'll review the patch, please wait for a while.

Thanks,
Kazu