netdev - 答复: [PATCH net-next] gen_estimator: change the lock order for better perfermance(Internet mail)

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Date:	Wed, 18 Sep 2013 05:41:09 +0000
From:	zhiguohong(洪志国) <zhiguohong@...cent.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Hong Zhiguo <honkiko@...il.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: 答复: [PATCH net-next] gen_estimator: change the lock order for better perfermance(Internet mail)

Actually I did try LOCKDEP and didn't get any warning.

Could you pointed out why it's wrong?

-----邮件原件-----
发件人: Eric Dumazet [mailto:eric.dumazet@...il.com] 
发送时间: 2013年9月17日 19:12
收件人: Hong Zhiguo
抄送: netdev@...r.kernel.org; davem@...emloft.net; stephen@...workplumber.org; zhiguohong(洪志国)
主题: Re: [PATCH net-next] gen_estimator: change the lock order for better perfermance(Internet mail)

On Tue, 2013-09-17 at 16:38 +0800, Hong Zhiguo wrote:
> From: Hong Zhiguo <zhiguohong@...cent.com>
> 
> e->stats_lock is usually taken by fast path to update stats.
> In the old order, fast path should wait for write_lock(&est_lock).
> Even though it's only one line inside the write_lock(&est_lock), but 
> if there's interrupt or page fault, a lot of spin on
> e->stats_lock will be wasted in fast path.

1) net-next is not open

2) There is no way a page fault can happen in this path.

3) This patch is wrong.

Current order is there for good reasons.

Have you really tried LOCKDEP, before sending a patch changing lock order ?