linux-kernel - Re: locking hierarchy based on lockdep

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Date:	Wed, 8 Nov 2006 00:53:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jason Baron <jbaron@...hat.com>
Cc:	linux-kernel@...r.kernel.org, arjan@...radead.org,
	rdreier@...co.com
Subject: Re: locking hierarchy based on lockdep


* Jason Baron <jbaron@...hat.com> wrote:

> > this would certainly be the simplest thing to do - we could extend 
> > /proc/lockdep with the list of 'immediately after' locks separated by 
> > commas. (that list already exists: it's the lock_class.locks_after list)
>
> So below is patch that does what you suggest, although i had to add 
> the concept of 'distance' to the patch since the locks_after list 
> loses this dependency info afaict. i also wrote a user space program 
> to sort the locks into cluster of interelated locks and then sorted 
> within these clusters...the results show one large clump of 
> locks...perhaps there are a few locks that time them all together like 
> scheduler locks...but i couldn't figure out which ones to exclude to 
> make the list look really pretty (also, there could be a bug in my 
> program :). Anyways i'm including my test program and its output 
> too...

nice!

small detail: i'm wondering why 'distance' is needed explicitly? The 
dependency graph as it is represented by locks_after should be a full 
representation of all locking dependencies. What is the intended 
definition of 'distance' - the distance from the root of the dependency 
tree? (Maybe i'm misunderstanding what you are trying to achieve.)

	Ingo
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