netdev - Re: [RFC V3 net-next 1/4] ethtool: add two coalesce attributes for CQE mode

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Message-ID: <9aad8548-8a3e-b88c-441f-805a0b71d709@huawei.com>
Date:   Mon, 16 Aug 2021 11:29:54 +0800
From:   moyufeng <moyufeng@...wei.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <shenjian15@...wei.com>, <lipeng321@...wei.com>,
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Subject: Re: [RFC V3 net-next 1/4] ethtool: add two coalesce attributes for
 CQE mode



On 2021/8/14 1:55, Jakub Kicinski wrote:
> On Fri, 13 Aug 2021 09:45:26 +0800 Yufeng Mo wrote:
>> Currently, there many drivers who support CQE mode configuration,
>> some configure it as a fixed when initialized, some provide an
>> interface to change it by ethtool private flags. In order make it
>> more generic, add two new 'ETHTOOL_A_COALESCE_USE_CQE_TX' and
>> 'ETHTOOL_A_COALESCE_USE_CQE_RX' coalesce attributes, then these
>> parameters can be accessed by ethtool netlink coalesce uAPI.
>>
>> Signed-off-by: Yufeng Mo <moyufeng@...wei.com>
>> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>
> 
> The series LGTM. When I was asking for documentation earlier I meant 
> a paragraph explaining the difference between the two modes. Here is 
> an example based on my current understanding, I could very well be
> wrong but you see what kind of explanation I'm after? If this is more
> or less correct please feel free to use it and modify as you see fit.
> 

The description in the following document is consistent with my
understanding. I'll add the following paragraph and add
"Signed-off-by: Jakub Kicinski <kuba@...nel.org>" to the patch.
Thanks for your correction.

> diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
> index c86628e6a235..fc7ac5938aac 100644
> --- a/Documentation/networking/ethtool-netlink.rst
> +++ b/Documentation/networking/ethtool-netlink.rst
> @@ -939,12 +939,25 @@ Gets coalescing parameters like ``ETHTOOL_GCOALESCE`` ioctl request.
>    ``ETHTOOL_A_COALESCE_TX_USECS_HIGH``         u32     delay (us), high Tx
>    ``ETHTOOL_A_COALESCE_TX_MAX_FRAMES_HIGH``    u32     max packets, high Tx
>    ``ETHTOOL_A_COALESCE_RATE_SAMPLE_INTERVAL``  u32     rate sampling interval
> +  ``ETHTOOL_A_COALESCE_USE_CQE_TX``            bool    timer reset mode, Tx
> +  ``ETHTOOL_A_COALESCE_USE_CQE_RX``            bool    timer reset mode, Rx
>    ===========================================  ======  =======================
>  
>  Attributes are only included in reply if their value is not zero or the
>  corresponding bit in ``ethtool_ops::supported_coalesce_params`` is set (i.e.
>  they are declared as supported by driver).
>  
> +Timer reset mode (``ETHTOOL_A_COALESCE_USE_CQE_TX`` and
> +``ETHTOOL_A_COALESCE_USE_CQE_RX``) control the interaction between packet
> +arrival and the various time based delay parameters. By default timers are
> +expected to limit the max delay between any packet arrival/departure
> +and a corresponding interrupt. In this mode timer should be started by packet
> +arrival (sometimes delivery of previous interrupt) and reset when interrupt
> +is delivered.
> +Setting the appropriate attribute to 1 will enable ``CQE`` mode, where
> +each packet event resets the timer. In this mode timer is used to force
> +the interrupt if queue goes idle, while busy queues depend on the packet
> +limit to trigger interrupts.
>  
>  COALESCE_SET
>  ============
> @@ -977,6 +990,8 @@ Sets coalescing parameters like ``ETHTOOL_SCOALESCE`` ioctl request.
>    ``ETHTOOL_A_COALESCE_TX_USECS_HIGH``         u32     delay (us), high Tx
>    ``ETHTOOL_A_COALESCE_TX_MAX_FRAMES_HIGH``    u32     max packets, high Tx
>    ``ETHTOOL_A_COALESCE_RATE_SAMPLE_INTERVAL``  u32     rate sampling interval
> +  ``ETHTOOL_A_COALESCE_USE_CQE_TX``            bool    timer reset mode, Tx
> +  ``ETHTOOL_A_COALESCE_USE_CQE_RX``            bool    timer reset mode, Rx
>    ===========================================  ======  =======================
>  
>  Request is rejected if it attributes declared as unsupported by driver (i.e.
> .
>