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

Wed, Mar 02, 2016 at 12:14:39PM CET, gerlitz.or@gmail.com wrote:

On Tue, Mar 1, 2016 at 7:01 PM, Jiri Pirko [off-list ref] wrote:

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Tue, Mar 01, 2016 at 05:49:27PM CET, amir@vadai.me wrote:

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On Tue, Mar 01, 2016 at 03:47:19PM +0100, Jiri Pirko wrote:

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Tue, Mar 01, 2016 at 03:24:43PM CET, amir@vadai.me wrote:

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This patch is based on a patch made by John Fastabend.

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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.

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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.

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Why? If a rule is offloaded, why would the user want to reprocess it by software?

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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.

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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.