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

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Date:	Wed, 22 Jun 2016 12:32:25 -0700
From:	Roopa Prabhu <roopa@...ulusnetworks.com>
To:	Jiri Pirko <jiri@...nulli.us>
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>
Subject: Re: [patch net-next v5 0/4] return offloaded stats as default and
 expose original sw stats

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 ?.
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.

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 .

Having a consistent model for all kinds of stats will help.