netdev - Re: [PATCH 0/2] net/sched: Add hardware specific counters to TC actions

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Date:   Sat, 11 Aug 2018 12:06:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jakub.kicinski@...ronome.com
Cc:     echaudro@...hat.com, netdev@...r.kernel.org, jhs@...atatu.com,
        xiyou.wangcong@...il.com, jiri@...nulli.us,
        simon.horman@...ronome.com
Subject: Re: [PATCH 0/2] net/sched: Add hardware specific counters to TC
 actions

From: Jakub Kicinski <jakub.kicinski@...ronome.com>
Date: Thu, 9 Aug 2018 20:26:08 -0700

> It is not immediately clear why this is needed.  The memory and
> updating two sets of counters won't come for free, so perhaps a
> stronger justification than troubleshooting is due? :S
> 
> Netdev has counters for fallback vs forwarded traffic, so you'd know
> that traffic hits the SW datapath, plus the rules which are in_hw will
> most likely not match as of today for flower (assuming correctness).
> 
> I'm slightly concerned about potential performance impact, would you
> be able to share some numbers for non-trivial number of flows (100k
> active?)?

Agreed, features used for diagnostics cannot have a harmful penalty for
fast path performance.