netdev - Re: [PATCHv2 net] net: restore lro after device detached from bridge

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Date:	Tue, 03 Feb 2015 10:29:00 +0800
From:	Fan Du <fengyuleidian0615@...il.com>
To:	Michal Kubecek <mkubecek@...e.cz>
CC:	Alexander Duyck <alexander.h.duyck@...hat.com>,
	Fan Du <fan.du@...el.com>, bhutchings@...arflare.com,
	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCHv2 net] net: restore lro after device detached from bridge

于 2015年02月02日 19:15, Michal Kubecek 写道:
> On Mon, Feb 02, 2015 at 10:20:12AM +0800, Fan Du wrote:
>>
>> I think you are talking about bad scenarios when net device is
>> attached to a bridge.  Then what's the good reason user has to pay
>> extra cpu power for using GRO, instead of using hw capable LRO/RSC
>> when this net device is detached from bridge acting as a standalone
>> NIC?
>
> Being bridged is only one of the situations when LRO needs to be
> disabled. Does your patch make sure it doesn't enable LRO if there are
> other reasons for it to be disabled, e.g. if forwarding is enabled for
> it or any of its upper devices?
>
> I'm afraid the only way to make the automatic reenabling work correctly
> would be to keep track if LRO was disabled manually (e.g. by ethtool) or
> only automatically because the device is bridged, forwarding is enabled
> for it, LRO is disabled for any upper device etc. And to reenable LRO
> only in the second case and even then only if none of the possible
> reasons holds. I don't think it's worth the effort.
>
>> Note, SRC is defaulted to *ON* in practice for ALL ixgbe NICs, as same
>> other RSC capable NICs.
>
> A very bad idea, IMHO. A lot of bug reports resulted from it.

Why are you saying this an idea?? this a fact for all RSC capable NIC drivers.
search drivers/net/ethernet/ to find more.

>> Attaching net device to a bridge _once_ should not changed its default
>> configuration, moreover it's a subtle change without any message that
>> user won't noticed at all.
> IMHO the key point here is that LRO enabled when it shouldn't is much
> more serious problem than LRO disabled when it could be enabled.

I agree with you here more than I disagree.
btw, I see this subtle behaviour not because I "seeing issues with routing or
bridging being enabled and" as Alexander assuming, it's because I see my testbed
82599EB supports LRO, and the driver enabled after probing from code review,
but for no reason ethtool -k reports lro is off, it looks like this interface
is bound to bridge by one of service.

>
>                                                         Michal Kubecek
>

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