netdev - Re: [PATCH take 2] pkt_sched: Fix qdisc_watchdog() vs. dev

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Date:	Tue, 16 Sep 2008 10:47:56 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	"Duyck, Alexander H" <alexander.h.duyck@...el.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Alexander Duyck <alexander.duyck@...il.com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kaber@...sh.net" <kaber@...sh.net>
Subject: Re: [PATCH take 2] pkt_sched: Fix qdisc_watchdog() vs.
	dev_deactivate() race

On Mon, Sep 15, 2008 at 04:44:08PM -0700, Duyck, Alexander H wrote:
...
> The only thing I really prefer about my solution as opposed to the solution
> Dave implemented was that it would mean only one dequeue instead of a peek
> followed by a dequeue.  I figure the important thing is to push the
> discovery of us being stopped to as soon as possible in the process.
> 
> It will probably be a few days before I have a patch with my approach ready.
> I didn't realize how complex it would be to resolve this issue for CBQ, HTB,
> HFSC, etc.  Also it is starting to look like I will probably need to implement
> another function to support this since it seems like the dequeue operations
> would need to be split into a multiqueue safe version, and a standard version
> to support some workarounds like those found in qdisc_peek_len() for HFSC.

Actually, looking at this HFSC now I start to doubt we need to
complicate these things so much. If HFSC is OK with its simple
hfsc_requeue() I doubt other qdiscs need much more, and we should
reconsider David's idea to do the same on top, in dev_requeue_skb().
Qdiscs like multiq would probably never use this, and these above
mentioned (not mq-optimized) qdiscs could be used with multiq if
needed. Then, it seems, it would be enough to improve multiq as a
"leaf" adding these dedicated operations and/or flags.

Thanks,
Jarek P.
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