rounding up CPUs on debug exception
geoffrey.levand at am.sony.com
Fri Sep 30 02:55:11 EST 2005
Paul Mackerras wrote:
> Geoff Levand writes:
>>When kgdb handles a debugging exception (trap or trace for ppc) it
>>tries to stop execution on the other CPUs as soon as possible so
>>that changes in the system state from the time of the exception
>>are minimized. The i386 code (below) uses the inter-processor
>>interrupt features of the APIC interrupt controller to send a
>>high priority NMI to the other CPUs. An NMI is needed here,
>>since another CPU may be waiting with interrupts disabled on a
>>spin lock the current cpu holds.
> Xmon uses smp_send_debugger_break(MSG_ALL_BUT_SELF) for this. It
> isn't an NMI, just a regular IPI, though.
Thanks for the tip. I used this and it works OK, although it seems
take a long time to sync under some conditions.
I noticed in your 'hotplug cpu on powermacs' post that powermacs have
the soft-reset pin connected to a GPIO port. When I have some time
I'll look into using this to send an NMI to the orher CPU's.
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