netdev - Re: [v5 Patch 1/3] netpoll: add generic support for bridge and bonding devices

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Date:	Tue, 08 Jun 2010 16:36:06 +0800
From:	Cong Wang <amwang@...hat.com>
To:	David Miller <davem@...emloft.net>
CC:	andy@...yhouse.net, fubar@...ibm.com, fbl@...close.org,
	linux-kernel@...r.kernel.org, mpm@...enic.com,
	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
	gospo@...hat.com, nhorman@...driver.com, jmoyer@...hat.com,
	shemminger@...ux-foundation.org,
	bonding-devel@...ts.sourceforge.net
Subject: Re: [v5 Patch 1/3] netpoll: add generic support for bridge and bonding
 devices

On 06/07/10 18:01, David Miller wrote:
> From: Cong Wang<amwang@...hat.com>
> Date: Mon, 07 Jun 2010 17:57:49 +0800
>
>> Hmm, I still feel like this way is ugly, although it may work.
>> I guess David doesn't like it either.
>
> Of course I don't like it. :-)
>
> I suspect the locking scheme will need to be changed.
>
> Besides, if we're going to hack this up and do write lock attempts in
> the read locking paths, there is no point in using a rwlock any more.
> And I'm personally in disfavor of all rwlock usage anyways (it dirties
> the cacheline for readers just as equally for writers, and if the
> critically protected code path is short enough, that shared cache
> line atomic operation will be the predominant cost).
>
> So I'd say, 1) make this a spinlock and 2) try to use RCU for the
> read path.
>
> That would fix everything.

Yeah, agreed. Even not talking about netconsole, bonding code
does have locking problems, netconsole just makes this problem
clear.

I will try your suggestions above.

Thanks!
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