netdev - Re: [PATCH net-next v2 4/4] net: hns3: support skb's frag page recycling based on page pool

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Date:   Wed, 8 Sep 2021 08:57:23 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     moyufeng <moyufeng@...wei.com>,
        Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
        alexander.duyck@...il.com, linux@...linux.org.uk, mw@...ihalf.com,
        linuxarm@...neuler.org, yisen.zhuang@...wei.com,
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        hawk@...nel.org, ast@...nel.org, daniel@...earbox.net,
        john.fastabend@...il.com, akpm@...ux-foundation.org,
        peterz@...radead.org, will@...nel.org, willy@...radead.org,
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        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, chenhao288@...ilicon.com
Subject: Re: [PATCH net-next v2 4/4] net: hns3: support skb's frag page
 recycling based on page pool

On Wed, 8 Sep 2021 18:26:35 +0300 Ilias Apalodimas wrote:
> > Normally I'd say put the stats in ethtool -S and the rest in debugfs
> > but I'm not sure if exposing pages_state_hold_cnt and
> > pages_state_release_cnt directly. Those are short counters, and will
> > very likely wrap. They are primarily meaningful for calculating
> > page_pool_inflight(). Given this I think their semantics may be too
> > confusing for an average ethtool -S user.
> > 
> > Putting all the information in debugfs seems like a better idea.  
> 
> I can't really disagree on the aforementioned stats being confusing.
> However at some point we'll want to add more useful page_pool stats (e.g the
> percentage of the page/page fragments that are hitting the recycling path).
> Would it still be 'ok' to have info split across ethtool and debugfs?

Possibly. We'll also see what Alex L comes up with for XDP stats. Maybe
we can arrive at a netlink API for standard things (broken record).

You said percentage - even tho I personally don't like it - there is a
small precedent of ethtool -S containing non-counter information (IOW
not monotonically increasing event counters), e.g. some vendors rammed
PCI link quality in there. So if all else fails ethtool -S should be
fine.