Date:   Thu, 9 Mar 2023 14:40:33 +0100
From:   Simon Horman <simon.horman@corigine.com>
To:     Leesoo Ahn <lsahn@ooseel.net>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        bpf@vger.kernel.org
Subject: Re: [PATCH net-next] net: stmmac: call stmmac_finalize_xdp_rx() on a
 condition
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References: <20230308162619.329372-1-lsahn@ooseel.net>
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On Thu, Mar 09, 2023 at 01:26:18AM +0900, Leesoo Ahn wrote:
> The current codebase calls the function no matter net device has XDP
> programs or not. So the finalize function is being called everytime when RX
> bottom-half in progress. It needs a few machine instructions for nothing
> in the case that XDP programs are not attached at all.
> 
> Lets it call the function on a condition that if xdp_status variable has
> not zero value. That means XDP programs are attached to the net device
> and it should be finalized based on the variable.
> 
> The following instructions show that it's better than calling the function
> unconditionally.
> 
>   0.31 │6b8:   ldr     w0, [sp, #196]
>        │    ┌──cbz     w0, 6cc
>        │    │  mov     x1, x0
>        │    │  mov     x0, x27
>        │    │→ bl     stmmac_finalize_xdp_rx
>        │6cc:└─→ldr    x1, [sp, #176]
> 
> with 'if (xdp_status)' statement, jump to '6cc' label if xdp_status has
> zero value.
> 
> Signed-off-by: Leesoo Ahn <lsahn@ooseel.net>

Hi Leesoo,

I am curious to know if you considered going a step further and using
a static key.

Link: https://www.kernel.org/doc/html/latest/staging/static-keys.html