Re: [PATCH] Add kallsyms_lookup() result cache

[Andi Kleen <ak@suse.de>]

On Fri, 18 Jun 2004 19:26:39 -0400
Jesse Barnes <jbarnes@engr.sgi.com> wrote:

> On Friday, June 18, 2004 6:03 pm, Andi Kleen wrote:
> > On Fri, 18 Jun 2004 15:03:00 -0500
> >
> > Brent Casavant <bcasavan@sgi.com> wrote:
> > > On 2.6 based systems, the top command utilizes /proc/[pid]/wchan to
> > > determine WCHAN symbol name information.  This information is provided
> > > by the kernel function kallsyms_lookup(), which expands a stem-compressed
> >
> > That sounds more like a bug in your top to me. /proc/*/wchan itself
> > does not access kallsyms, it just outputs a number.undisclosed-recipients:;
> 
> No, it outputs a string:
> jbarnes@mill:~$ cat /proc/1/wchan
> do_select

Indeed. I looked at /proc/self/wchan, but of course that is 0 because
the process is running. 

But there is numerical wchan anyways - just get it from /proc/*/stat
That is what all 2.4 based tops always used.  I bet they still
have the fallback code for that around.The 2.6 change 
will just be to read the symbol table from /proc/kallsyms instead
of from the System.map file.

> 
> > Doing the cache in the kernel is the wrong place. This should be fixed
> > in user space.
> 
> Sure, but that would be a change in behavior.  It's arguably the right thing 
> to do though.

Change what behaviour? I argue that doing it in the kernel is the wrong
thing.

-Andi