netdev - Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

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Date:	Wed, 27 Jun 2012 11:23:34 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, hans.schillstrom@...csson.com,
	subramanian.vijay@...il.com, dave.taht@...il.com,
	netdev@...r.kernel.org, ncardwell@...gle.com, therbert@...gle.com,
	mph@...h.dk
Subject: Re: [PATCH v2 net-next] tcp: avoid tx starvation by SYNACK packets

On Wed, 2012-06-27 at 10:45 +0200, Eric Dumazet wrote:
> On Wed, 2012-06-27 at 10:21 +0200, Jesper Dangaard Brouer wrote:
> 
> > It works because we have a spinlock problem in the code... Perhaps, they
> > did it, because we have have locking/contention problem, not the other
> > way around ;-)  How about fixing the code instead? ;-)))
> 
> The socket lock is currently mandatory.
>
> It's really _hard_ to remove it, your attempts added a lot of races.

Yes, its really hard to remove completely.  That's why I choose _only_
to handle the SYN cookie "overload" case, and leave the rest locked, and
I also introduced extra locking in the latest patches.  I know it was
not perfect, hence the RFC tag, but I hope I didn't add that many races.


> I want to do it properly, adding needed RCU and array of spinlocks were
> appropriate.

I really appreciate that you will attempt to fix this properly.  Like a
real network ninja ;-).


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