netdev - Re: [PATCH 3/3] gianfar: remove faulty filer optimizer

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Date:	Tue, 11 Aug 2015 11:41:31 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	moorray3@...pl
Cc:	claudiu.manoil@...escale.com, netdev@...r.kernel.org,
	kubakici@...pl
Subject: Re: [PATCH 3/3] gianfar: remove faulty filer optimizer

From: Jakub Kiciński <moorray3@...pl>
Date: Tue, 11 Aug 2015 16:51:09 +0200

> On Tue, 11 Aug 2015 14:00:23 +0000, Manoil Claudiu wrote:
>> >-----Original Message-----
>> >From: Jakub Kicinski [mailto:moorray3@...pl]
>> >Sent: Monday, August 10, 2015 11:12 PM
>> >To: David S. Miller; Manoil Claudiu-B08782
>> >Cc: netdev@...r.kernel.org; Jakub Kicinski
>> >Subject: [PATCH 3/3] gianfar: remove faulty filer optimizer
>> >
>> >From: Jakub Kicinski <kubakici@...pl>
>> >
>> >Current filer rule optimization is broken in several ways:
>> > (1) It destroys rule ordering.
>> > (2) It performs reads/writes beyond end of allocated tables.
>> > (3) It breaks badly for rules with more than 2 specifiers
>> >     (e.g. matching ip, port, tos).
>> > (4) We observed that the masking rules it generates do not
>> >     play well with clustering on P2020.  Only first rule
>> >     of the cluster would ever fire.  Given that optimizer
>> >     relies heavily on masking this is very hard to fix.
>> >
>> >The fact that nobody noticed (1), (3) or (4) makes me think
>> >that this feature is not very widely used and we should just
>> >remove it.
>> 
>> I'm not familiar with this filer classification code and its
>> author is no longer active apparently.   There is not much of a
>> choice here since this optimization feature is too complex and
>> poorly documented to be reviewed and validated in a reasonable
>> time span.
>> An example, a simple use case showing expected behavior vs.
>> actual behavior would help.
> 
> Sure, sorry, should be part of the submission quite honestly...

I think removing this optimizer is the thing to do as well.

Please respin this patch series with the examples added to the
commit message of patch #3.

Thanks.
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