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

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Message-ID: <508E6783.2080403@unimore.it>
Date:	Mon, 29 Oct 2012 12:24:51 +0100
From:	Paolo Valente <paolo.valente@...more.it>
To:	Cong Wang <xiyou.wangcong@...il.com>
CC:	jhs@...atatu.com, davem@...emloft.net, shemminger@...tta.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	rizzo@....unipi.it, fchecconi@...il.com
Subject: Re: [PATCH RFC] pkt_sched: enable QFQ to support TSO/GSO

Il 29/10/2012 12:08, Cong Wang ha scritto:
> On 10/29/2012 04:51 PM, Paolo Valente 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 (a notification is also appended
>> to the log).
>>
>> 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>
>
>
> Please respect people who helps you to test it:
>
> Tested-by: Cong Wang <amwang@...hat.com>
Oops, really sorry about that. I did not mean to hide your contribution. 
I am just not familiar with the process.
>
> I tested it again just in case...
Thanks again
>
> By the way, one nit below:
>
>
>> +    if (unlikely(cl->lmax < qdisc_pkt_len(skb))) {
>> +        pr_notice("qfq: increasing maxpkt from %u to %u for class %u",
>> +              cl->lmax, qdisc_pkt_len(skb), cl->common.classid);
>> +        qfq_update_reactivate_class(q, cl, cl->inv_w,
>> +                        qdisc_pkt_len(skb), 0);
>> +    }
>
>
> Seems the log level KERN_NOTICE is overkill, normal users don't care
> about these information, so s/pr_notice/pr_debug/.
>
Thanks, I will integrate this and possible other suggestions in a new 
version of the patch.
>
> Thanks!
>
>


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