netdev - Re: [RFC PATCH net-next] qfq: handle the case that front slot is empty

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Date:	Sun, 28 Oct 2012 17:07:13 +0100
From:	Paolo Valente <paolo.valente@...more.it>
To:	Cong Wang <amwang@...hat.com>
Cc:	netdev@...r.kernel.org, Stephen Hemminger <shemminger@...tta.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Fabio Checconi <fchecconi@...il.com>
Subject: Re: [RFC PATCH net-next] qfq: handle the case that front slot is empty


Il giorno 28/ott/2012, alle ore 13:45, Cong Wang ha scritto:

> On Fri, 2012-10-26 at 18:51 +0200, Paolo Valente wrote:
>> Here is a possible patch. Could you please give me a feedback?
>> 
>> If this patch actually works, there are some issues related to it that I would
>> like to point out after your (and/or anyone else's) tests.
> 
> With this patch applied, I can't reproduce the crash any more.
Thank you for the test.
> 
> And the following messages appear in the log:
> 
> [  430.956400] qfq: increasing class max_pkt_size from 1514 to 26130
> [  430.981887] qfq: increasing class max_pkt_size from 26130 to 31922
> [  431.011844] qfq: increasing class max_pkt_size from 1514 to 2962
> [  431.060129] qfq: increasing class max_pkt_size from 31922 to 46402
> [  431.096241] qfq: increasing class max_pkt_size from 2962 to 4410
> [  431.123689] qfq: increasing class max_pkt_size from 4410 to 18890
> [  431.134624] qfq: increasing class max_pkt_size from 18890 to 20338
> [  431.149573] qfq: increasing class max_pkt_size from 20338 to 39162
> [  431.328157] qfq: increasing class max_pkt_size from 46402 to 56538
> [  431.339731] qfq: increasing class max_pkt_size from 56538 to 65226
> [  431.363699] qfq: increasing class max_pkt_size from 39162 to 44954
> [  431.376303] qfq: increasing class max_pkt_size from 44954 to 46402
> [  431.482082] qfq: increasing class max_pkt_size from 46402 to 62330
> [  431.520339] qfq: increasing class max_pkt_size from 62330 to 65226
> 
> 
WIth each of these messages, qfq now informs the user that he/she has chosen a too low max_pkt_size with respect to the actual size of the last-arrived packet, and that the max_pkt_size has been increased automatically to handle this larger packet correctly. In the log that you report, the large packets that cause qfq to increase the max_pkt_size are due to TSO/GSO.

Any feedback about these notifications is welcome. Meanwhile I will prepare a description of the patch and of the limitations it imposes.--
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