reason for "magic" crashes.

[Mateusz Guzik]

On Sun, Jun 24, 2012 at 08:50:41PM +0200, Wojciech Puchar wrote:
> >>
> >>
> >>There is nothing in cron that is done at sunday.
> >>
> >>i don't run "periodic" stuff in /etc/crontab
> >>
> >
> >Compile the kernel with the following:
> >
> >makeoptions     DEBUG="-O0 -g"
> >
> >options         KDB                     # Enable kernel debugger support.
> >options         DDB                     # Support DDB.
> >options         GDB                     # Support remote GDB.
> >options         DEADLKRES               # Enable the deadlock resolver
> >options         INVARIANTS              # Enable calls of extra sanity checking
> >options         INVARIANT_SUPPORT       # Extra sanity checks of internal structures, required by INVARIANTS
> >options         WITNESS                 # Enable checks to detect deadlocks and cycles
> >options         WITNESS_SKIPSPIN        # Don't run witness on spinlocks for speed
> >options         DIAGNOSTIC
> >
> >After kernel panic ddb prompt will be waiting for you. Type in:
> >dump <enter>
> >reset <enter>
> >
> >Make sure you have swap that can handle crashdumps.
> 
> already did this part and debug part, but not DDB. As you see - hang
> not crashdump
> 
> how much would it slow down whole thing?
> 
> If less than 2 times it can be - CPU are rerely half loaded

Are you asking about overhead of DDB or all debug options?

I don't think that DDB support can be accounted for slowdown.

As for the rest, it's hard to say. I guess it depends on your workload,
also I never performed any benchmarks to compare this and I'm unaware of
any.

In other words, you have to test it yourself.

-- 
Mateusz Guzik <mjguzik gmail.com>