linux-kernel - Re: [PATCH net-next] net: ethernet: mlx4: Avoid assigning a value to ring_cons but not used it anymore in mlx4_en

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Message-Id: <20200913.143308.2042080994542358655.davem@davemloft.net>
Date:   Sun, 13 Sep 2020 14:33:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ttoukan.linux@...il.com
Cc:     luojiaxing@...wei.com, kuba@...nel.org, idos@...lanox.com,
        ogerlitz@...lanox.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com
Subject: Re: [PATCH net-next] net: ethernet: mlx4: Avoid assigning a value
 to ring_cons but not used it anymore in mlx4_en_xmit()

From: Tariq Toukan <ttoukan.linux@...il.com>
Date: Sun, 13 Sep 2020 13:12:05 +0300

> 
> 
> On 9/13/2020 4:22 AM, David Miller wrote:
>> From: Luo Jiaxing <luojiaxing@...wei.com>
>> Date: Sat, 12 Sep 2020 16:08:15 +0800
>> 
>>> We found a set but not used variable 'ring_cons' in mlx4_en_xmit(), it
>>> will
>>> cause a warning when build the kernel. And after checking the commit
>>> record
>>> of this function, we found that it was introduced by a previous patch.
>>>
>>> So, We delete this redundant assignment code.
>>>
>>> Fixes: 488a9b48e398 ("net/mlx4_en: Wake TX queues only when there's
>>> enough room")
>>>
>>> Signed-off-by: Luo Jiaxing <luojiaxing@...wei.com>
>> Looks good, applied, thanks.
>> 
> 
> Hi Luo,
> 
> I didn't get a chance to review it during the weekend.

Tariq, what are you even commenting on?  Are you responding to this patch
which removes a %100 obviously unused variable set, or on the commit
mentioned in the Fixes: tag?

> The ring_cons local variable is used in line 903:
> https://elixir.bootlin.com/linux/v5.9-rc4/source/drivers/net/ethernet/mellanox/mlx4/en_tx.c#L903

He is removing an assignment to ring_cons much later in the function
and therefore has no effect on this line.

> 1. Your patch causes a degradation to the case when MLX4_EN_PERF_STAT
> is defined.

This is not true, see above.