On Wed, Jan 6, 2010 at 7:04 PM, Dimitrios Apostolou <jimis@gmx.net> wrote:
On Sat, 14 Nov 2009, Dimitrios Apostolou wrote:
Hello list,
is anyone actually getting WCHAN information from either ps or top? To try it just use "ps opid,wchan,cmd". I only get dashes, any idea why?
I managed to resolve this issue. Arch builds its kernels (on 32-bit at least) without CONFIG_FRAME_POINTER and loses the ability to produce correct stacktraces, either with /proc/$PID/wchan or with SysRq-t or with gdb. On the other hand it has one more register free so minor optimisations can be performed.
Why don't we set CONFIG_FRAME_POINTER=y? WCHAN output is very useful to be lost and frankly I don't think performance losses would be perceivable. Last but not least I haven't seen this disabled in any other distro.
Sorry for not answering earlier, but I probably did not have any ideas when reading your previous answers. I am on 64-bit and I have the same result here using Arch kernel. The reason why it worked for me and still works is that I am always using a custom kernel, I use http://cgit.freedesktop.org/nouveau/linux-2.6/ to follow nouveau development. And I have CONFIG_FRAME_POINTER=y because this option is quite important indeed <<< If you say Y here the resulting kernel image will be slightly larger and slower, but it gives very useful debugging information in case of kernel bugs. (precise oopses/stacktraces/warnings) >>> I definitely want to get precise oopses/stacktraces/warnings so that I can report them if needed. Maybe the average arch user also wants to do that, I don't know. You can do some research to find out what the big distrib are using in their default kernel (fedora,suse,debian,ubuntu,...) and/or you can open a bug in Flyspray.