netdev - Re: [RFC net-next 02/13] net: page_pool: avoid touching slow on the fastpath

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Message-ID: <CAHS8izO-OYz5RR1uk0E7oG+0kfr6PmkeJ5QTD7JrcmKcN2K4nQ@mail.gmail.com>
Date: Thu, 17 Aug 2023 14:31:46 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, hawk@...nel.org, ilias.apalodimas@...aro.org, 
	aleksander.lobakin@...el.com, linyunsheng@...wei.com
Subject: Re: [RFC net-next 02/13] net: page_pool: avoid touching slow on the fastpath

On Wed, Aug 16, 2023 at 4:43 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> To fully benefit from previous commit add one byte of state
> in the first cache line recording if we need to look at
> the slow part.
>
> The packing isn't all that impressive right now, we create
> a 7B hole. I'm expecting Olek's rework will reshuffle this,
> anyway.
>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
>  include/net/page_pool/types.h | 2 ++
>  net/core/page_pool.c          | 4 +++-
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
> index 1c16b95de62f..1ac7ce25fbd4 100644
> --- a/include/net/page_pool/types.h
> +++ b/include/net/page_pool/types.h
> @@ -127,6 +127,8 @@ struct page_pool_stats {
>  struct page_pool {
>         struct page_pool_params_fast p;
>
> +       bool has_init_callback;
> +

Nit: I wonder if it's slightly more appropriate for this to be
has_slow, given how I understand the intent of usage, but it doesn't
really matter. Either way,:

Reviewed-by: Mina Almasry <almasrymina@...gle.com>

>         long frag_users;
>         struct page *frag_page;
>         unsigned int frag_offset;
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index ffe7782d7fc0..2c14445a353a 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -216,6 +216,8 @@ static int page_pool_init(struct page_pool *pool,
>             pool->p.flags & PP_FLAG_PAGE_FRAG)
>                 return -EINVAL;
>
> +       pool->has_init_callback = !!pool->slow.init_callback;
> +
>  #ifdef CONFIG_PAGE_POOL_STATS
>         pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
>         if (!pool->recycle_stats)
> @@ -373,7 +375,7 @@ static void page_pool_set_pp_info(struct page_pool *pool,
>  {
>         page->pp = pool;
>         page->pp_magic |= PP_SIGNATURE;
> -       if (pool->slow.init_callback)
> +       if (pool->has_init_callback)
>                 pool->slow.init_callback(page, pool->slow.init_arg);
>  }
>
> --
> 2.41.0
>


-- 
Thanks,
Mina