Date:	Mon, 27 Jun 2016 08:51:02 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:	Anuradha Karuppiah <anuradhak@...ulusnetworks.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	Nogah Frankel <nogahf@...lanox.com>,
	Ido Schimmel <idosch@...lanox.com>,
	Elad Raz <eladr@...lanox.com>,
	Yotam Gigi <yotamg@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
	John Linville <linville@...driver.com>,
	Thomas Graf <tgraf@...g.ch>,
	Andy Gospodarek <gospo@...ulusnetworks.com>,
	Scott Feldman <sfeldma@...il.com>, sd@...asysnail.net,
	eranbe@...lanox.com, Alexei Starovoitov <ast@...mgrid.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"hannes@...essinduktion.org" <hannes@...essinduktion.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	David Ahern <dsa@...ulusnetworks.com>
Subject: Re: [patch net-next v5 0/4] return offloaded stats as default and
 expose original sw stats

Mon, Jun 27, 2016 at 04:53:53AM CEST, roopa@...ulusnetworks.com wrote:
>On Sun, Jun 26, 2016 at 11:15 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>> Sun, Jun 26, 2016 at 08:06:40PM CEST, roopa@...ulusnetworks.com wrote:
>>>On 6/26/16, 2:33 AM, Jiri Pirko wrote:
>>>> Sat, Jun 25, 2016 at 05:50:59PM CEST, roopa@...ulusnetworks.com wrote:
>>>>> On Thu, Jun 23, 2016 at 8:40 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>>>> Thu, Jun 23, 2016 at 05:11:26PM CEST, anuradhak@...ulusnetworks.com wrote:
>>>>>>>>>>> we can't separate CPU and HW stats there. In some cases (or ASICs) HW
>>>>>>>>>>> counters do
>>>>>>>>>>> not include CPU generated packets....you will have to add CPU
>>>>>>>>>>> generated pkt counters to the
>>>>>>>>>>> hw counters for such virtual device stats.
>>>>>>>>>> Can you please provide and example how that could happen?
>>>>>>>>> example is the bridge vlan stats I mention below. These are usually counted
>>>>>>>>> by attaching hw virtual counter resources. And CPU generated packets
>>>>>>>>> in some cases maybe setup to bypass the ASIC pipeline because the CPU
>>>>>>>>> has already made the required decisions. So, they may not be counted by
>>>>>>>>> by such hw virtual counters.
>>>>>>>> Bypass ASIC? How do the packets get on the wire?
>>>>>>>>
>>>>>>> Bypass the "forwarding pipeline" in the ASIC that is. Obviously the
>>>>>>> ASIC ships the CPU generated packet out of the switch/front-panel
>>>>>>> port. Continuing Roopa's example of vlan netdev stats.... To get the
>>>>>>> HW stats counters are typically tied to the ingress and egress vlan hw
>>>>>>> entries. All the incoming packets are subject to the ingress vlan
>>>>>>> lookup irrespective of whether they get punted to the CPU or whether
>>>>>>> they are forwarded to another front panel port. In that case the
>>>>>>> ingress HW stats does represent all packets. However for CPU
>>>>>>> originated packets egress vlan lookups are bypassed in the ASIC (this
>>>>>>> is common forwarding option in most ASICs) and the packet shipped as
>>>>>>> is out of front-panel port specified by the CPU. Which means these
>>>>>>> packets will NOT be counted against the egress VLAN HW counter; hence
>>>>>>> the need for summation.
>>>>>> Driver will know about this, and will provide the stats accordignly to
>>>>>> the core. Who else than driver should resolve this.
>>>>>>
>>>>> The point was/is that there should be only two categories:
>>>>> 1) the base default stats: can contain 'only sw', 'only hw' or 'a
>>>>> summation of hw and sw' in some cases.
>>>>> The user does not care about the breakdown.
>>>>>
>>>>> 2) everything else falls into the second category: driver provided
>>>>> breakdown of stats for easier debugging.
>>>>> This today is ethtool stats and we can have an equivalent nested
>>>>> attribute for this in the new stats api.
>>>>> Lets call it IFLA_STATS_LINK_DRIVER or you pick a name. Lets make it
>>>>> nested and extensible (like ethtool is) and
>>>>> driver can expose any kind of stats there.
>>>>> ie lets move the stats you are proposing to this category of stats.....
>>>>> instead of introducing a third category 'SW stats'.
>>>> What you are proposing is essentially what our patchset does. We expose
>>>> 2 sets of stats. hw and pure sw. hw includes all, driver will take
>>>> care of it cause he knows what is going on in hw.
>>>the splitting into hw and sw is causing some confusion with respect
>>
>> I still don't get why you are talking about split :( I see no split.
>>
>>
>>>to existing stats and will be confusing for future stats. And i am not sure how many
>>>users would prefer the split this way.
>>>So, instead of doing the split, i think we should at this time introduce
>>>driver specific stats (like ethtool) as a nested netlink attribute.
>>
>> The default netlink stats should be hw (or accumulated as you call it).
>> The reason is to avoid confusion for existing apps. Another attribute is
>> possible for more break-out stats - that is what this patchset is doing.
>>
>> Ethtool stats are wrong and useless for apps as they are driver-specific.
>
>apps only care about overall stats. thats the aggregate stats
>provided by the default netlink netdev api to the user...which already exists.
>
>they don't care about your new breakdown either.

Agreed. That is what our patchset is doing.


>
>breakdown of stats are used for debugging and thats what ethtool stats provide.
>
>
>
>>
>>
>>>>
>>>> Btw mirroring random string stats into Netlink is not a good idea IMO.
>>>Any reason you say that ?. I am thinking it would be much easier with netlink.
>>>keeping it simple, it is a nested attribute with stat-name and value pair.
>>>
>>>struct stat {
>>>    char stats_name[STATS_NAME_LEN];    /* STATS_NAME_LEN = 32 */
>>>    __u64 stat;
>>>};
>>
>> No please. This should be well defined generic group of stats.
>> Driver-specific names/stats stats are wrong.
>>
>
>they are meant for debugging. are you saying the new stats api should
>not contain 'ethtool like' stats ?
>
>ethtool stats are very valuable today. They are extensible.
>They cannot be made generic and they are specific to a hardware or use case.
>
>We use it for our switch port stats too. Base aggregate stats summed
>up and provided as default netdev stats. via ethtool we provide lot
>more hardware specific breakdown.

Leave it in ethtool then. I really think it is not idea to put random
named-stats in netlink.

This patchset uses well defined values for slowpatch(/sw/cpu) stats.
That is I believe the only way to do this.

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