netdev - Re: [PATCH BUGFIX] pkt_sched: sch_qfq: remove a source of high packet delay/jitter

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Message-Id: <20130718.130335.991768032324737210.davem@davemloft.net>
Date:	Thu, 18 Jul 2013 13:03:35 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	paolo.valente@...more.it
Cc:	jhs@...atatu.com, shemminger@...tta.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, fchecconi@...il.com,
	rizzo@....unipi.it
Subject: Re: [PATCH BUGFIX] pkt_sched: sch_qfq: remove a source of high
 packet delay/jitter

From: Paolo Valente <paolo.valente@...more.it>
Date: Tue, 16 Jul 2013 08:52:30 +0200

 ...
> This patch addresses this issue by just using the above
> 'instantaneous' value of the weight sum, instead of the maximum
> possible value, when updating the system virtual time.  After the
> instantaneous weight sum is decreased, QFQ+ may deviate from the ideal
> service for a time interval in the order of the time to serve one
> maximum-size packet for each backlogged class. The worst-case extent
> of the deviation exhibited by QFQ+ during this time interval [1] is
> basically the same as of the deviation described above (but, without
> this patch, QFQ+ suffers from such a deviation all the time). Finally,
> this patch modifies the comment to the function qfq_slot_insert, to
> make it coherent with the fact that the weight sum used by QFQ+ can
> now be lower than the maximum possible value.
> 
> [1] P. Valente, "Extending WF2Q+ to support a dynamic traffic mix",
> Proceedings of AAA-IDEA'05, June 2005.
> 
> Signed-off-by: Paolo Valente <paolo.valente@...more.it>

Thank you for this amazing commit message.

Since you explained everything, even if I don't understand all of the
details of QFQ/QFQ+ I can in fact be confident in your change.

Applied and queued up for -stable, thanks!
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