Message-ID: <e75d2a42-4154-e469-bbd7-9409471ab724@ooseel.net>
Date:   Fri, 10 Mar 2023 00:08:29 +0900
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Subject: Re: [PATCH net-next] net: stmmac: call stmmac_finalize_xdp_rx() on a
 condition
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To:     Simon Horman <simon.horman@corigine.com>
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
References: <20230308162619.329372-1-lsahn@ooseel.net>
 <ZAnh0TGtDkVUl/1m@corigine.com>
From:   Leesoo Ahn <lsahn@ooseel.net>
In-Reply-To: <ZAnh0TGtDkVUl/1m@corigine.com>
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On 23. 3. 9. 22:40, Simon Horman wrote:
> 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

Thank you for the review.

The function must be called for only XDP_TX or XDP_REDIRECT cases.
So using a static key doesn't look good and the commit message is not 
clear for 'why' as well.
I think that's why you suggested for using 'static key' by the latter 
reason.

I will edit the message and post v2 soon.

Best regards,
Leesoo