netdev - Re: [PATCH net-next 1/8] net/flower: Introduce hardware offload support

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Date:	Wed, 2 Mar 2016 14:22:22 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Or Gerlitz <gerlitz.or@...il.com>
Cc:	John Fastabend <john.r.fastabend@...el.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Amir Vadai <amir@...ai.me>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Saeed Mahameed <saeedm@...lanox.com>,
	Hadar Har-Zion <hadarh@...lanox.com>,
	Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH net-next 1/8] net/flower: Introduce hardware offload
 support

Wed, Mar 02, 2016 at 12:14:39PM CET, gerlitz.or@...il.com wrote:
>On Tue, Mar 1, 2016 at 7:01 PM, Jiri Pirko <jiri@...nulli.us> wrote:
>> Tue, Mar 01, 2016 at 05:49:27PM CET, amir@...ai.me wrote:
>>>On Tue, Mar 01, 2016 at 03:47:19PM +0100, Jiri Pirko wrote:
>>>> Tue, Mar 01, 2016 at 03:24:43PM CET, amir@...ai.me wrote:
>>>> >This patch is based on a patch made by John Fastabend.
>
>>>> >It adds support for offloading cls_flower.
>>>> >A filter that is offloaded successfully by hardware, will not be added to
>>>> >the hashtable and won't be processed by software.
>
>>>> That is wrong. User should explicitly specify to not include rule into sw
>>>> by SKIP_KERNEL flag (does not exist now, with John's recent patch we'll
>>>> have only SKIP_HW). Please add that in this patchset.
>
>>> Why? If a rule is offloaded, why would the user want to reprocess it by software?
>
>>> If the user use SKIP_HW, it will be processed by SW. Else, the user
>>> would want it to be processed by HW or fallback to SW. I don't
>>> understand in which case the user would like to have it done twice.
>
>> For example if you turn on the offloading by unsetting NETIF_F_HW_TC.
>> Or if someone inserts skbs into rx path directly, for example pktgen.
>> We need SKIP_KERNEL to be set by user, not implicit.
>
>As discussed in netdev, we want to have three modes for TC offloads
>
>1. SW only
>2. HW only (and err if can't)
>3. HW and if not supported fallback to SW
>
>Now, from your reply, I understand we want a fourth mode
>
>4. Both (HW and SW)

I would perhaps do it a litte bit differently:
NO FLAG (default)- insert into kernel and HW now:
		if NETIF_F_HW_TC is off (default)
			-> push to kernel only (current behaviour)
		if NETIF_F_HW_TC is on AND push to HW fails
			-> return error
SKIP_HW - flag to tell kernel not to insert into HW
SKIP_SW - flag to tell kernel not to insert into kernel

to achieve hw only, user has to turn on the NETIF_F_HW_TC and
pass SKIP_SW flag.


>
>Do we agree that these four policies/modes make sense?
>
>So you want #4 to be the default? can you elaborate why? note that for
>the HW marking
>case a "both" mode will be very inefficient, also for actions like
>vlan push/pop, encap/decap, etc

Well when you push/pop vlan of encap/decap tunnel header in hw, you won't
match the packet in kernel again. Most likely. But anyway, if you turn
on NETIF_F_HW_TC you know what you are doing and you adjust the
included rules (flags) accordingly.


>the result will be just wrong... I don't think this should be the default.
>
>Or.