netdev - Re: [patch net-next v4 0/4] return offloaded stats as default and expose original sw stats

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Message-ID: <20160618080000.GA1989@nanopsycho.orion>
Date:	Sat, 18 Jun 2016 10:00:00 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	David Ahern <dsa@...ulusnetworks.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	nogahf@...lanox.com, idosch@...lanox.com, eladr@...lanox.com,
	yotamg@...lanox.com, ogerlitz@...lanox.com,
	roopa@...ulusnetworks.com, nikolay@...ulusnetworks.com,
	linville@...driver.com, tgraf@...g.ch, gospo@...ulusnetworks.com,
	sfeldma@...il.com, sd@...asysnail.net, eranbe@...lanox.com,
	ast@...mgrid.com, edumazet@...gle.com, hannes@...essinduktion.org
Subject: Re: [patch net-next v4 0/4] return offloaded stats as default and
 expose original sw stats

Fri, Jun 17, 2016 at 07:12:22PM CEST, f.fainelli@...il.com wrote:
>On 06/17/2016 08:42 AM, Jiri Pirko wrote:
>> Fri, Jun 17, 2016 at 05:35:53PM CEST, dsa@...ulusnetworks.com wrote:
>>> On 6/17/16 8:54 AM, Jamal Hadi Salim wrote:
>>>> On 16-06-17 10:05 AM, Jiri Pirko wrote:
>>>>> Fri, Jun 17, 2016 at 03:48:35PM CEST, dsa@...ulusnetworks.com wrote:
>>>>>> On 6/17/16 2:24 AM, Jiri Pirko wrote:
>>>>>>>
>>>>
>>>>>
>>>>> That is problematic. Existing apps depend on rtnetlink stats. But if we
>>>>> don't count offloaded forwarded packets, the apps don't see anything.
>>>>> Therefore I believe that this patchset approach is better. The existing
>>>>> apps continue to work and future apps can use newly introduces sw_stats
>>>>> to query slowpath traffic. Makes sense to me.
>>>>>
>>>>
>>>> I agree with Jiri. It is a bad idea to depend on ethtool for any of
>>>> this stuff. Is there a way we can tag netlink stats instead
>>>> to indicate they are hardware or software?
>>>
>>> Right, old API but the key here is that low level h/w stats are returned by a
>>> different API.
>>>
>>> By default ip, ifconfig, snmpd, etc all continue to get traditional S/W stats
>>> - counters as seen by the CPU.
>> 
>> Yep. And I believe that for offloaded forwarding, this tools should see
>> hw counters, as they show what is going on in real.
>
>If your NIC is offloading packets today, these tools typically won't see
>these stats, but ethtool -S likely will report what is going on under
>the hood.
>
>Do we actually need to tell apart SW maintained from HW maintained
>stats, or at the end all that matters is just, as DaveM pointed out,
>getting the information, and in the case of an Ethernet switch, return
>HW stats by default and supplement with SW stats whenever we have them,
>all in the same namespace?

I believe it is valuable for user to know stats for slow path
(non-forwarded by ASIC). Also, it's just another rtnl attr. Easy.