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SubjectRe: [RFC,PATCH 2/2] perf, x86: Utilize the LBRs for machine/oops debugging

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, 2010-03-29 at 19:02 +0200, Ingo Molnar wrote:
>
> > Plus, it would be nice to have a sysctl entry for this as well - so that
> > production systems can enable this if they want to enrich the output of
> > some difficult-to-analyze kernel crash, without yet another reboot.
>
> Right, could do, but once it crashed it clearly to late to enable anything
> ;-)

No. What i mean is that with your patch, a debugging session would go like
this:

< kernel crashes > # reboot #1
< admin logs in and scratches head >
< admin consults kernel hackers and enables lbr_debug=1 in /etc/grub.conf >

< admin reboots > # reboot #2
< kernel crashes again > # reboot #3
With the sysctl we'd have one reboot less:

< kernel crashes > # reboot #1
< admin logs in and scratches head >
< admin consults kernel hackers and tweaks /proc/sys/kernel/x86/lbr_debug >

< kernel crashes again > # reboot #2
Thanks,

Ingo


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