netdev - Re: [PATCH net-next] gen_estimator: change the lock order for better perfermance

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Message-ID: <1379416308.29845.11.camel@edumazet-glaptop>
Date:	Tue, 17 Sep 2013 04:11:48 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hong Zhiguo <honkiko@...il.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	stephen@...workplumber.org, Hong Zhiguo <zhiguohong@...cent.com>
Subject: Re: [PATCH net-next] gen_estimator: change the lock order for
 better perfermance

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 ?



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