netdev - Re: [PATCH] sch_sfq: revert dont put new flow at the end of flows

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Message-Id: <20120316.015625.2065025946513016046.davem@davemloft.net>
Date:	Fri, 16 Mar 2012 01:56:25 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	jdb@...x.dk, dave.taht@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] sch_sfq: revert dont put new flow at the end of flows

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 13 Mar 2012 21:04:25 -0700

> This reverts commit d47a0ac7b6 (sch_sfq: dont put new flow at the end of
> flows)
> 
> As Jesper found out, patch sounded great but has bad side effects.
> 
> In stress situation, pushing new flows in front of the queue can prevent
> old flows doing any progress. Packets can stay in SFQ queue for
> unlimited amount of time.
> 
> It's possible to add heuristics to limit this problem, but this would
> add complexity outside of SFQ scope.
> 
> A more sensible answer to Dave Taht concerns (who reported the issued I
> tried to solve in original commit) is probably to use a qdisc hierarchy
> so that high prio packets dont enter a potentially crowded SFQ qdisc.
> 
> Reported-by: Jesper Dangaard Brouer <jdb@...x.dk>
> Cc: Dave Taht <dave.taht@...il.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Applied, thanks Eric.
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