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

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Message-ID: <YTjqIOt5+0J0r2bg@apalos.home>
Date:   Wed, 8 Sep 2021 19:51:44 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     moyufeng <moyufeng@...wei.com>,
        Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
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Subject: Re: [PATCH net-next v2 4/4] net: hns3: support skb's frag page
 recycling based on page pool

On Wed, Sep 08, 2021 at 08:57:23AM -0700, Jakub Kicinski wrote:
> 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.

Yea percentage may have been the wrong example. I agree that having
absolute numbers (all allocated pages and recycled pages) is a better
option.  To be honest keeping the 'weird' stats in debugfs seems sane, the 
pages_state_hold_cnt/pages_state_release_cnt are only going to be needed
during debug.


Thanks
/Ilias