netdev - Re: [PATCH v3 net-next 0/3] flow_offload: Re-add per-action statistics

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Date:   Thu, 23 May 2019 10:25:13 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Edward Cree <ecree@...arflare.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        "Cong Wang" <xiyou.wangcong@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Michael Chan <michael.chan@...adcom.com>,
        Vishal Kulkarni <vishal@...lsio.com>
Subject: Re: [PATCH v3 net-next 0/3] flow_offload: Re-add per-action
 statistics

On Thu, 23 May 2019 17:40:08 +0100, Edward Cree wrote:
> On 23/05/2019 17:11, Jakub Kicinski wrote:
> > On Thu, 23 May 2019 09:19:49 -0400, Jamal Hadi Salim wrote:  
> >> That would still work here, no? There will be some latency
> >> based on the frequency of hardware->kernel stats updates.  
> > I don't think so, I think the stats are only updated on classifier
> > dumps in Ed's code.  
> Yep currently that's the case, but not as an inherent restriction (see
>  my other mail).

I think we can all agree that the current stats offload only reporting
up-to-date HW stats when classifiers are dumped makes slight mockery of
the kernel API guarantees.  I feel like HW vendors found a subset of
the ABI to poke things in and out of the hardware, and things work
correctly if you limit yourself to that very subset.  So you only get
up-to-date stats if you dump classifiers, if you dump actions - no dice.

Whether it's on you to fix this is debatable :)  Since you're diving
into actions and adding support for shared ones, I'd say it's time to
rectify the situation.

Let's look at it this way - if you fix the RTM_GETACTION you will
necessarily add the cookie and all the other stuff you need in your
upcoming driver :)

> > But we can't be 100% sure without seeing driver code.  
> Would it help if I posted my driver code to the list?  It's gonna be
>  upstream eventually anyway, it's just that the driver as a whole
>  isn't really in a shape to be merged just yet (mainly 'cos the
>  hardware folks are planning some breaking changes).  But I can post
>  my TC handling code, or even the whole driver, if demonstrating how
>  these interfaces can be used will help matters.

From my perspective - you answered the question so I'm at 100% now ;)