netdev - Re: [PATCH RFC] pkt_sched: enable QFQ to support TSO/GSO

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Date:	Mon, 5 Nov 2012 16:41:49 +0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Paolo Valente <paolo.valente@...more.it>, jhs@...atatu.com,
	David Miller <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	rizzo@....unipi.it, fchecconi@...il.com
Subject: Re: [PATCH RFC] pkt_sched: enable QFQ to support TSO/GSO

On Tue, Oct 30, 2012 at 10:24 PM, Stephen Hemminger
<shemminger@...tta.com> wrote:
> On Tue, 30 Oct 2012 07:00:56 +0100
> Paolo Valente <paolo.valente@...more.it> wrote:
>
>> Hi,
>> if the max packet size for some class (configured through tc) is
>> violated by the actual size of the packets of that class, then QFQ
>> would not schedule classes correctly, and the data structures
>> implementing the bucket lists may get corrupted. This problem occurs
>> with TSO/GSO even if the max packet size is set to the MTU, and is,
>> e.g., the cause of the failure reported in [1]. Two patches have been
>> proposed to solve this problem in [2], one of them is a preliminary
>> version of this patch.
>>
>> This patch addresses the above issues by: 1) setting QFQ parameters to
>> proper values for supporting TSO/GSO (in particular, setting the
>> maximum possible packet size to 64KB), 2) automatically increasing the
>> max packet size for a class, lmax, when a packet with a larger size
>> than the current value of lmax arrives.
>>
>> The drawback of the first point is that the maximum weight for a class
>> is now limited to 4096, which is equal to 1/16 of the maximum weight
>> sum.
>>
>> Finally, this patch also forcibly caps the timestamps of a class if
>> they are too high to be stored in the bucket list. This capping, taken
>> from QFQ+ [3], handles the unfrequent case described in the comment to
>> the function slot_insert.
>>
>> [1] http://marc.info/?l=linux-netdev&m=134968777902077&w=2
>> [2] http://marc.info/?l=linux-netdev&m=135096573507936&w=2
>> [3] http://marc.info/?l=linux-netdev&m=134902691421670&w=2
>>
>> Signed-off-by: Paolo Valente <paolo.valente@...more.it>
>> Tested-by: Cong Wang <amwang@...hat.com>
>
> Acked-by: Stephen Hemminger <shemminger@...tta.com>


David, could you take this patch? Stephen acked it.

Thanks!
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