linux-kernel - Re: BUG-lockdep and freeze (was: Arrr! Linux 2.6.18)

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Date:	Sat, 30 Sep 2006 22:49:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Andi Kleen <ak@...e.de>, Eric Rannaud <eric.rannaud@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, nagar@...son.ibm.com,
	Chandra Seetharaman <sekharan@...ibm.com>,
	Jan Beulich <jbeulich@...ell.com>
Subject: Re: BUG-lockdep and freeze (was: Arrr! Linux 2.6.18)

* Linus Torvalds <torvalds@...l.org> wrote:

> I mean, really: Andi, point me to anything that was a real problem 
> when we had no unwinder at all?

personally, i like perfect stacktraces, alot. x86_64 was a huge pain for 
me without the unwinder. I got so used to perfect backtraces on i686 
(when using %ebp frames) during the years, and i had to look at _many_ 
backtraces with lockdep. On x86_64 it was just constant brain-drain to 
think away bogus stack entries. Yes, i can do it no problem when i have 
to look at only a few stacktraces per day, but if it's hundreds per day 
it's _alot_ of brainpower wasted.

(i'd have been happy with an %rbp based unwinder for x86_64, in fact i 
implemented it for lockdep and used it for some time on x86_64, but Andi 
wanted a dwarf-based, lower-overhead one. Andi also nicely integrated it 
into stacktrace.c.)

	Ingo
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