Planned availability of SGI kdb and lkcd in future 2.4 vendor dis tributions

[Marc Esipovich]

On Fri, Sep 08, 2000 at 09:49:52AM +1100, Keith Owens wrote:
> On Thu, 7 Sep 2000 15:33:20 -0700 (PDT), 
> Scott Lurndal <slurn at nanobiz.com> wrote:
> >Being that there is no additional overhead (aside from some small number
> >of kb of code) when KDB is included in a production kernel, it is nice
> >to have on all the time - just in case the system does panic or hang
> >due to a heisenbug.
> 
> It does introduce overhead on some common paths.
> 
> * NMI handling checks for a kdb vector, NMI code is driven once per
>   timer tick on each cpu if the NMI oopser is active (which it should
>   be).
> 
> * The serial code has to check for kdb interrupt keys.
> 
> * The frame pointer option adds extra code to some assembler code like
>   semaphore and spin lock out of line code.
> 
> * The register spill affect of maintaining frame pointers on ix86 is
>   noticable, fortunately kdb v1.3 works without frame pointers so I
>   normally run without CONFIG_FRAME_POINTER.
> 
> * kdb has a longer section of code for the page fault handler, we have
>   to handle last branch recording around the page fault code.  This is
>   the one that worries me the most as far as performance goes.
> 
> * kdb needs kallsyms to get kernel and module symbols.  kallsyms adds
>   20-30% to the size of the loaded kernel.
> 
> * The main kdb code itself increases the size of the kernel, although
>   this is swamped by the size of kallsyms.

I don't think all of these are really relevent, because kdb should be under
the 'kernel hacking' section and kdb will only be used by ones who need it.

It's just a nice thing to have in the kernel.

OTOH, LKCD is a must, of course as an option too, but no system is complete
w/o some sort of crashdump features and crashdump analysis tools.

This is a feature every trustworthy kernel should provide.

 bye,
	Marc.

--
marc @ corky.net

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