linux-kernel - Re: [PATCH net v1] net: stmmac: set PP_FLAG_DMA_SYNC

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Message-ID: <7bbeed88-5ad1-41c1-a742-8a1737eb7ffa@redhat.com>
Date: Thu, 19 Sep 2024 12:25:48 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Furong Xu <0x1207@...il.com>, Ong Boon Leong <boon.leong.ong@...el.com>,
 "David S. Miller" <davem@...emloft.net>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jose Abreu <joabreu@...opsys.com>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Maxime Coquelin
 <mcoquelin.stm32@...il.com>, Joao Pinto <jpinto@...opsys.com>
Cc: netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 rmk+kernel@...linux.org.uk, linux@...linux.org.uk, xfr@...look.com
Subject: Re: [PATCH net v1] net: stmmac: set PP_FLAG_DMA_SYNC_DEV only if XDP
 is enabled

On 9/13/24 13:02, Furong Xu wrote:
> When XDP is not enabled, the page which holds the received buffer
> will be recycled once the buffer is copied into SKB by
> skb_copy_to_linear_data(), then the MAC core will never reuse this
> page any longer. Set PP_FLAG_DMA_SYNC_DEV wastes CPU cycles.
> 
> This patch brings up to 9% noticeable performance improvement on
> certain platforms.
> 
> Fixes: 5fabb01207a2 ("net: stmmac: Add initial XDP support")
> Signed-off-by: Furong Xu <0x1207@...il.com>

I'm quite unconvinced that every performance improvement would be 
eligible to be considered a fix.

Reading the code it looks like this change actually addresses a 
regression introduced by the blamed commit, is that correct? If so 
please re-phrase the commit message accordingly.

Thanks,

Paolo