linux-kernel - Re: [tip:core/locking 1/3] lockdep:reintroduce generation count to make BFS faster

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Message-ID: <d82e647a0907220617p5055ef3bu7f396eda3ac27fa@mail.gmail.com>
Date:	Wed, 22 Jul 2009 21:17:56 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...e.hu, torvalds@...ux-foundation.org
Subject: Re: [tip:core/locking 1/3] lockdep:reintroduce generation count to 
	make BFS faster

2009/7/22 Peter Zijlstra <a.p.zijlstra@...llo.nl>:
> On Wed, 2009-07-22 at 20:58 +0800, tom.leiming@...il.com wrote:
>> From: Ming Lei <tom.leiming@...il.com>
>>
>> We still can apply DaveM's generation count optimization to
>> BFS, so reintroduce it.
>
> Please elaborate, changelogs are important.

Sorry, I'll resend the patches and provide a elaborate changlogs.


>
> You fail to explain why it still applies and what the gains are.
>
> (I can guess, but you explaining makes sure we're on the same page)
>

gains:
        1), avoid to allocate the bfs_accessed array;

        2), remove the
                    bitmap_zero(bfs_accessed, MAX_LOCKDEP_ENTRIES);
              in each BFS, which is a little time consuming since
MAX_LOCKDEP_ENTRIES
              is very large.(16384UL)

-- 
Lei Ming
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