netdev - Re: [PATCH v6 net-next 4/5] net: page_pool: make stats available just for global pools

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Message-ID: <877cjpzfgv.fsf@toke.dk>
Date: Wed, 31 Jan 2024 16:32:00 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>, Jesper Dangaard Brouer
 <hawk@...nel.org>
Cc: Yunsheng Lin <linyunsheng@...wei.com>, Lorenzo Bianconi
 <lorenzo@...nel.org>, netdev@...r.kernel.org, davem@...emloft.net,
 kuba@...nel.org, edumazet@...gle.com, pabeni@...hat.com,
 bpf@...r.kernel.org, willemdebruijn.kernel@...il.com, jasowang@...hat.com,
 sdf@...gle.com, ilias.apalodimas@...aro.org
Subject: Re: [PATCH v6 net-next 4/5] net: page_pool: make stats available
 just for global pools

Lorenzo Bianconi <lorenzo.bianconi@...hat.com> writes:

>> 
>> 
>> On 30/01/2024 14.52, Lorenzo Bianconi wrote:
>> > > On 2024/1/29 21:07, Lorenzo Bianconi wrote:
>> > > > > On 2024/1/28 22:20, Lorenzo Bianconi wrote:
>> > > > > > Move page_pool stats allocation in page_pool_create routine and get rid
>> > > > > > of it for percpu page_pools.
>> > > > > 
>> > > > > Is there any reason why we do not need those kind stats for per cpu
>> > > > > page_pool?
>> > > > > 
>> > > > 
>> > > > IIRC discussing with Jakub, we decided to not support them since the pool is not
>> > > > associated to any net_device in this case.
>> > > 
>> > > It seems what jakub suggested is to 'extend netlink to dump unbound page pools'?
>> > 
>> > I do not have a strong opinion about it (since we do not have any use-case for
>> > it at the moment).
>> > In the case we want to support stats for per-cpu page_pools, I think we should
>> > not create a per-cpu recycle_stats pointer and add a page_pool_recycle_stats field
>> > in page_pool struct since otherwise we will endup with ncpu^2 copies, right?
>> > Do we want to support it now?
>> > 
>> > @Jakub, Jesper: what do you guys think?
>> > 
>> 
>> 
>> I do see an need for being able to access page_pool stats for all
>> page_pool's in the system.
>> And I do like Jakub's netlink based stats.
>
> ack from my side if you have some use-cases in mind.
> Some questions below:
> - can we assume ethtool will be used to report stats just for 'global'
>   page_pool (not per-cpu page_pool)?
> - can we assume netlink/yaml will be used to report per-cpu page_pool stats?
>
> I think in the current series we can fix the accounting part (in particular
> avoiding memory wasting) and then we will figure out how to report percpu
> page_pool stats through netlink/yaml. Agree?

Deferring the export API to a separate series after this is merged is
fine with me. In which case the *gathering* of statistics could also be
deferred (it's not really useful if it can't be exported).

-Toke