netdev - Re: [PATCH net] net: flow_offload: skip hw stats check for FLOW_ACTION_HW_STATS

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Message-ID: <20200420135754.GD32392@breakpoint.cc>
Date:   Mon, 20 Apr 2020 15:57:54 +0200
From:   Florian Westphal <fw@...len.de>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Edward Cree <ecree@...arflare.com>,
        netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, kuba@...nel.org
Subject: Re: [PATCH net] net: flow_offload: skip hw stats check for
 FLOW_ACTION_HW_STATS_DISABLED

Jiri Pirko <jiri@...nulli.us> wrote:
> Mon, Apr 20, 2020 at 02:39:15PM CEST, pablo@...filter.org wrote:
> >On Mon, Apr 20, 2020 at 01:28:22PM +0100, Edward Cree wrote:
> >> On 20/04/2020 12:52, Jiri Pirko wrote:
> >> > However for TC, when user specifies "HW_STATS_DISABLED", the driver
> >> > should not do stats.
> >>
> >> What should a driver do if the user specifies DISABLED, but the stats
> >>  are still needed for internal bookkeeping (e.g. to prod an ARP entry
> >>  that's in use for encapsulation offload, so that it doesn't get
> >>  expired out of the cache)?  Enable the stats on the HW anyway but
> >>  not report them to FLOW_CLS_STATS?  Or return an error?
> >
> >My interpretation is that HW_STATS_DISABLED means that the front-end
> >does not care / does not need counters. The driver can still allocate
> 
> That is wrong interpretation. If user does not care, he specifies "ANY".
> That is the default.
> 
> When he says "DISABLED" he means disabled. Not "I don't care".

Under what circumstances would the user care about this?
Rejecting such config seems to be just to annoy user?

I mean, the user is forced to use SW datapath just because HW can't turn
off stats?!  Same for a config change, why do i need to change my rules
to say 'enable stats' even though I don't need them in first place?

Unlike the inverse (want feature X but HW can't support it), it makes
no sense to me to reject with an error here:
stats-off is just a hint that can be safely ignored.