netdev - Re: [PATCH net-next 0/6] net: page_pool: Add page

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Date:   Thu, 27 Jan 2022 11:08:50 +0200
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Joe Damato <jdamato@...tly.com>
Cc:     netdev@...r.kernel.org, kuba@...nel.org, davem@...emloft.net,
        hawk@...nel.org
Subject: Re: [PATCH net-next 0/6] net: page_pool: Add page_pool stat counters

Hi Joe, 

On Wed, Jan 26, 2022 at 02:48:14PM -0800, Joe Damato wrote:
> Greetings:
> 
> This series adds some stat counters for the page_pool allocation path which
> help to track:
> 
> 	- fast path allocations
> 	- slow path order-0 allocations
> 	- slow path high order allocations
> 	- refills which failed due to an empty ptr ring, forcing a slow
> 	  path allocation
> 	- allocations fulfilled via successful refill
> 	- pages which cannot be added to the cache because of numa mismatch
> 	  (i.e. waived)
> 

Thanks for the patch.  Stats are something that's indeed missing from the
API.  The patch  should work for Rx based allocations (which is what you
currently cover),  since the RX side is usually protected by NAPI.  However
we've added a few features recently,  which we would like to have stats on. 

commit 6a5bcd84e886("page_pool: Allow drivers to hint on SKB recycling"),
introduces recycling capabilities on the API.  I think it would be far more
interesting to be able to extend the statistics to recycled/non-recycled
packets as well in the future.  But the recycling is asynchronous and we
can't add locks just for the sake of accurate statistics.  Can we instead
convert that to a per-cpu structure for producers?

Thanks!
/Ilias

> Some static inline wrappers are provided for accessing these stats. The
> intention is that drivers which use the page_pool API can, if they choose,
> use this stats API.
> 
> It assumed that the API consumer will ensure the page_pool is not destroyed
> during calls to the stats API.
> 
> If this series is accepted, I'll submit a follow up patch which will export
> these stats per RX-ring via ethtool in a driver which uses the page_pool
> API.
> 
> Joe Damato (6):
>   net: page_pool: Add alloc stats and fast path stat
>   net: page_pool: Add a stat for the slow alloc path
>   net: page_pool: Add a high order alloc stat
>   net: page_pool: Add stat tracking empty ring
>   net: page_pool: Add stat tracking cache refills.
>   net: page_pool: Add a stat tracking waived pages.
> 
>  include/net/page_pool.h | 82 +++++++++++++++++++++++++++++++++++++++++++++++++
>  net/core/page_pool.c    | 15 +++++++--
>  2 files changed, 94 insertions(+), 3 deletions(-)
> 
> -- 
> 2.7.4
>