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Subject: Re: [RFC PATCH 00/12] locking/lockdep: Add a new class of terminal
 locks
References: <1541709268-3766-1-git-send-email-longman@redhat.com>
 <20181109080412.GC86700@gmail.com>
 <20181110141045.GD3339@worktop.programming.kicks-ass.net>
From: Waiman Long <longman@redhat.com>
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Date: Sat, 10 Nov 2018 18:35:57 -0500
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To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>, Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>, Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Tejun Heo <tj@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>

On 11/10/2018 09:10 AM, Peter Zijlstra wrote:
> On Fri, Nov 09, 2018 at 09:04:12AM +0100, Ingo Molnar wrote:
>> BTW., if you are interested in more radical approaches to optimize 
>> lockdep, we could also add a static checker via objtool driven call graph 
>> analysis, and mark those locks terminal that we can prove are terminal.
>>
>> This would require the unified call graph of the kernel image and of all 
>> modules to be examined in a final pass, but that's within the principal 
>> scope of objtool. (This 'final pass' could also be done during bootup, at 
>> least in initial versions.)
> Something like this is needed for objtool LTO support as well. I just
> dread the build time 'regressions' this will introduce :/
>
> The final link pass is already by far the most expensive part (as
> measured in wall-time) of building a kernel, adding more work there
> would really suck :/

I think the idea is to make objtool have the capability to do that. It
doesn't mean we need to turn it on by default in every build.

Cheers,
Longman