netdev - Re: [patch net-next 00/10] net: allow user specify TC filter HW stats type

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Message-ID: <20200222063829.GB2228@nanopsycho>
Date:   Sat, 22 Feb 2020 07:38:29 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, saeedm@...lanox.com,
        leon@...nel.org, michael.chan@...adcom.com, vishal@...lsio.com,
        jeffrey.t.kirsher@...el.com, idosch@...lanox.com,
        aelior@...vell.com, peppe.cavallaro@...com,
        alexandre.torgue@...com, jhs@...atatu.com,
        xiyou.wangcong@...il.com, pablo@...filter.org, mlxsw@...lanox.com,
        Edward Cree <ecree@...arflare.com>
Subject: Re: [patch net-next 00/10] net: allow user specify TC filter HW
 stats type

Fri, Feb 21, 2020 at 07:22:00PM CET, kuba@...nel.org wrote:
>On Fri, 21 Feb 2020 10:56:33 +0100 Jiri Pirko wrote:
>> From: Jiri Pirko <jiri@...lanox.com>
>> 
>> Currently, when user adds a TC filter and the filter gets offloaded,
>> the user expects the HW stats to be counted and included in stats dump.
>> However, since drivers may implement different types of counting, there
>> is no way to specify which one the user is interested in.
>> 
>> For example for mlx5, only delayed counters are available as the driver
>> periodically polls for updated stats.
>> 
>> In case of mlxsw, the counters are queried on dump time. However, the
>> HW resources for this type of counters is quite limited (couple of
>> thousands). This limits the amount of supported offloaded filters
>> significantly. Without counter assigned, the HW is capable to carry
>> millions of those.
>> 
>> On top of that, mlxsw HW is able to support delayed counters as well in
>> greater numbers. That is going to be added in a follow-up patch.
>> 
>> This patchset allows user to specify one of the following types of HW
>> stats for added fitler:
>> any - current default, user does not care about the type, just expects
>>       any type of stats.
>> immediate - queried during dump time
>> delayed - polled from HW periodically or sent by HW in async manner
>> disabled - no stats needed
>
>Hmm, but the statistics are on actions, it feels a little bit like we
>are perpetuating the mistake of counting on filters here.

You are right, the stats in tc are per-action. However, in both mlxsw
and mlx5, the stats are per-filter. What hw_stats does is that it
basically allows the user to set the type for all the actions in the
filter at once. 

Could you imagine a usecase that would use different HW stats type for
different actions in one action-chain?

Plus, if the fine grained setup is ever needed, the hw_stats could be in
future easilyt extended to be specified per-action too overriding
the per-filter setup only for specific action. What do you think?


>
>Would it not work to share actions between filters which don't need
>fine grained stats if HW can do more filters than stats?

For mlxsw it would work, if the action chain would be identical. For
that you don't need the per-action granularity of setting type hw_stats.

>
>Let's CC Ed on this.
>