Re: [PATCH] net/i40e: enable statistic reset for VF

-----Original Message-----
From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
Sent: Monday, March 20, 2017 5:14 PM
To: Zhang, Helin
Cc: Zhang, Qi Z; techboard@dpdk.org; dev@dpdk.org; Wu, Jingjing; Yigit,
Ferruh; Liang, Cunming; Fastabend, John R
Subject: Re: [dpdk-dev] [PATCH] net/i40e: enable statistic reset for VF

2017-03-20 02:47, Zhang, Helin:

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From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]

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2017-03-17 09:45, Zhang, Helin:

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From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]

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2017-03-17 03:28, Zhang, Helin:

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From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]

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2017-02-23 13:27, Qi Zhang:

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 static void
+i40evf_dev_stats_reset(struct rte_eth_dev *dev) {
+	struct i40e_vf *vf = I40EVF_DEV_PRIVATE_TO_VF(dev->data-
dev_private);
+	/* only DPDK PF support this */
+	if (vf->version_major == I40E_DPDK_VERSION_MAJOR) {
+		if (i40evf_reset_statistics(dev))
+			PMD_DRV_LOG(ERR, "Reset statistics failed");
+	}
+}

One more SR-IOV feature not supported with a Linux PF.
The basic stats feature must be marked as partially supported in
	doc/guides/nics/features/i40e_vf.ini
See also this email:
	http://dpdk.org/ml/archives/dev/2017-March/060063.html

I wonder whether we should allow such divergence between PF
implementations. Intel committed to avoid such fragmentation
and keep the SR-IOV messaging standard but it does not happen.
It is said that we must allow fast innovation in DPDK space.
I agree but we should also target a good usability of the VF
drivers, allowing to replace the PF implementations as needed.

Hi Thomas

I think I need to clarify a little bit here.
I think we will try our best, but I don't think we can commit.
As they are on totally different community, and of cause code

repositories.

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What prevent you from submitting your code to the kernel community?
Note that your statement does not respect the agreed policy:
	http://dpdk.org/ml/archives/dev/2017-January/055224.html
	http://dpdk.org/doc/guides/contributing/design.html#pf-and-vf-
considerations

There might be some confusing or misunderstanding.
I didn't say we will not submit any patches to kernel community.
We will try to send a few first, and then see what will happen. If it
will be rejected, or take too much time to be accepted. Then we may give up.
If it can be accepted by kernel community, then we may continue.
That's the reality, we will try, but we cannot make any commitment on
having anything in kernel side.

Of course you do not know if it will be accepted in Linux.
The agreed policy was just to try:
"
PF functionality should only be added to DPDK for testing and prototyping
purposes while the kernel work is ongoing.
"

OK. I understood. I am sure we will try soon with few first. So we are aligned. Thanks!

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Here is my suggestion: let's accept a VF feature only if the
PF support is submitted to both dpdk.org and kernel.org mailing lists.
I ask to add this topic to the next techboard meeting.

Sorry, technically I disagree with this suggestion, as I don't
understand

why!

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I was told DPDK is not Linux, and Linux is not DPDK. Why we
want to add this dependency on Linux PF host driver? And why
just on PF/VF

driver feature only?

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I think if we can have any good innovative idea on DPDK first,
why not just have it on DPDK? Then Linux or even other
OS/community/Company can learn from DPDK and develop their own.

It is really a general problem.
Here you are adding a feature in a VF driver. But it does not
work with some PF drivers.We have the same problem when adding a
feature which does not work on BSD or on a CPU architecture.
Generally speaking, we have a usability issue when a feature
works only with a given environment.
And it is worst in the SR-IOV case because a VM can migrate from
an hypervisor (with a given PF) to another (and different) one.

Yes, I understood that's the reality and the issue. But I don't
think we can

address it with your suggestion.

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Linux is just one of the OS, as you said, FreeBSD, Windows, VMWare,  ...

I am talking about migration from a KVM to another one.
So BSD, Windows and VMware are irrelevant.

But as a guest user, he may want to his application running well in
all the VMs without modifying anything, no matter in KVM, Windows, or

VMWare.

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Do you want to address that issue too?

That's a different question. DPDK PF is a replacement for Linux PF.
When considering another hypervisor (Windows or VMware), there can be
many things different. I think trying to have the same behaviour, with all these
hypervisors, is a nice goal but a smaller priority than DPDK/Linux
standardization.

So you are suggesting to have the VF drivers with the same behaviours
between kernel host driver and DPDK host driver, right?
Nothing about kernel side live migration, nothing about link bonding, right?

Then I have thoughts as below.
- Frist, applications with using that VF should work well no matter with using
  kernel host or DPDK host driver, as long as the VF application can handle
  the return value gracefully. For example, if kernel host does not support a
  VF request, while DPDK host supports, the kernel driver will return with an
  error code to indicate that is not supported, and the VF application should
  handle that well and smartly. I don't think it will block anything. Any different
  view on that?
- Second, will there really have any desire to move from DPDK host to kernel host?
  I don't see there is any desire to do that, and we can add restriction there.
- Third, even two KVMs with different version of kernel driver, it may not work,
  as different version of kernel drivers have different features and capabilities.
  So we cannot assume it works the same way between two KVMs with different
  kernel driver versions.

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I'd suggest to start another discussion on the tech board to solve
that problem, but not limit adding new features. They are
different topics

and things, based on my understanding.

Helin, you just want to add your new code and hide issues.
You don't even bother to document the limitations or the partial
support as I have suggested earlier.
As a maintainer, I have to check the quality and the usability.
I can tell you that I stack the promises "I will fix it later" and
we are still waiting for a lot of them.
That's why, even if you think it is not related, we need sometimes
to block things until they are properly done and completed.

There is no doubt, I appreciate your great job!
As I said before, we will try to submit a few first, and see what will happen.
For your doc requests, I think somebody else already replied you.

Sorry, I don't know that you are thinking about KVM migration. I was
informed by Vincent that all DPDK PF host features should be
consistent with kernel host driver, though I am not sure if I missed anything.
OK. Let's focus on the issue. What's the problem statement? What's the
solution well discussed and accepted widely by the community?
BTW, do we need to think about that a bit more? For example, do we
need to think about the similar policy on rte_flow API, ACL and possibly other

features?

Yes homogeneity should be general, so we must keep it in mind for future
works and enhancements of every DPDK areas.
We could write some general guidelines that the techboard would have to
approve.

Yes, a lot of issues or limitations even not just on DPDK needs to be addressed.
That's the great job the community maintainers and developers are working on.
Yes, doc update is always we need to do better. Thank you very much!

/Helin