netdev - Re: [PATCH net-next 06/11] net: page_pool: avoid calling no-op externals when possible

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Date: Wed, 17 May 2023 21:08:04 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Maciej Fijalkowski
 <maciej.fijalkowski@...el.com>, Magnus Karlsson
 <magnus.karlsson@...el.com>, Michal Kubiak <michal.kubiak@...el.com>,
 Larysa Zaremba <larysa.zaremba@...el.com>, Jesper Dangaard Brouer
 <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>,
 Christoph Hellwig <hch@....de>, netdev@...r.kernel.org,
 intel-wired-lan@...ts.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 06/11] net: page_pool: avoid calling no-op
 externals when possible

On Tue, 16 May 2023 18:18:36 +0200 Alexander Lobakin wrote:
> +		/* Try to avoid calling no-op syncs */
> +		pool->p.flags |= PP_FLAG_DMA_MAYBE_SYNC;
> +		pool->p.flags &= ~PP_FLAG_DMA_SYNC_DEV;
>  	}
>  
>  	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
> @@ -323,6 +327,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
>  
>  	page_pool_set_dma_addr(page, dma);
>  
> +	if ((pool->p.flags & PP_FLAG_DMA_MAYBE_SYNC) &&
> +	    dma_need_sync(pool->p.dev, dma)) {
> +		pool->p.flags |= PP_FLAG_DMA_SYNC_DEV;
> +		pool->p.flags &= ~PP_FLAG_DMA_MAYBE_SYNC;
> +	}

is it just me or does it feel cleaner to allocate a page at init,
and throw it into the cache, rather than adding a condition to a
fast(ish) path?