netdev - Re: [patch net-next v5 0/4] return offloaded stats as default and expose original sw stats

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Date:	Thu, 23 Jun 2016 13:35:08 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:	"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>,
	Anuradha Karuppiah <anuradhak@...ulusnetworks.com>
Subject: Re: [patch net-next v5 0/4] return offloaded stats as default and
 expose original sw stats

Thu, Jun 23, 2016 at 01:27:35PM CEST, roopa@...ulusnetworks.com wrote:
>On 6/22/16, 10:40 PM, Jiri Pirko wrote:
>> Wed, Jun 22, 2016 at 09:32:25PM CEST, roopa@...ulusnetworks.com wrote:
>>> On Tue, Jun 21, 2016 at 8:15 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>> From: Jiri Pirko <jiri@...lanox.com>
>>>>
>>>> The problem we try to handle is about offloaded forwarded packets
>>>> which are not seen by kernel. Let me try to draw it:
>>>>
>>>>     port1                       port2 (HW stats are counted here)
>>>>       \                          /
>>>>        \                        /
>>>>         \                      /
>>>>          --(A)---- ASIC --(B)--
>>>>                     |
>>>>                    (C)
>>>>                     |
>>>>                    CPU (SW stats are counted here)
>>>>
>>>>
>>>> Now we have couple of flows for TX and RX (direction does not matter here):
>>>>
>>>> 1) port1->A->ASIC->C->CPU
>>>>
>>>>    For this flow, HW and SW stats are equal.
>>>>
>>>> 2) port1->A->ASIC->C->CPU->C->ASIC->B->port2
>>>>
>>>>    For this flow, HW and SW stats are equal.
>>>>
>>>> 3) port1->A->ASIC->B->port2
>>>>
>>>>    For this flow, SW stats are 0.
>>>>
>>>> The purpose of this patchset is to provide facility for user to
>>>> find out the difference between flows 1+2 and 3. In other words, user
>>>> will be able to see the statistics for the slow-path (through kernel).
>>>>
>>>> Also note that HW stats are what someone calls "accumulated" stats.
>>>> Every packet counted by SW is also counted by HW. Not the other way around.
>>>>
>>>> As a default the accumulated stats (HW) will be exposed to user
>>>> so the userspace apps can react properly.
>>>>
>>>>
>>> curious, how do you plan to handle virtual device counters like vlan
>>> and vxlan stats ?.
>> Yes, that is another problem (1). We have to push stats up to this devices
>> most probably. But that problem is orthogonal to this. To the user, you
>> will still need 2 sets of stats and HW stats being default. So this
>> patchset infra is going to be used as well.
>hmm...But, i don't think we should start adding different tlv's hw and sw for
>every stats variant we add.
>>
>>
>>> 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?


>
>>
>>
>>> example: In the switchdev model, for bridge vlan stats, when user
>>> queries bridge vlan stats,
>>> you will have to add the hw stats to the bridge driver vlan stats and
>>> return it to the user .
>> Yep, that is (1).
>
>unless i misunderstood, this does not look like (1). In (1) you say hw stats
> already reflect sw stats. But in this case, hw counter does not include sw stats
>for CPU generated packets.
>>
>>
>>> Having a consistent model for all kinds of stats will help.
>