netdev - Re: [RFC net-next 2/4] ethtool: extend coalesce setting uAPI with CQE mode

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Date:   Wed, 26 May 2021 17:00:33 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Huazhong Tan <tanhuazhong@...wei.com>
Cc:     <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <salil.mehta@...wei.com>, <yisen.zhuang@...wei.com>,
        <huangdaode@...wei.com>, <linuxarm@...wei.com>,
        <dledford@...hat.com>, <jgg@...pe.ca>, <netanel@...zon.com>,
        <akiyano@...zon.com>, <thomas.lendacky@....com>,
        <irusskikh@...vell.com>, <michael.chan@...adcom.com>,
        <edwin.peer@...adcom.com>, <rohitm@...lsio.com>,
        <jesse.brandeburg@...el.com>, <jacob.e.keller@...el.com>,
        <ioana.ciornei@....com>, <vladimir.oltean@....com>,
        <sgoutham@...vell.com>, <sbhatta@...vell.com>, <saeedm@...dia.com>,
        <ecree.xilinx@...il.com>, <grygorii.strashko@...com>,
        <merez@...eaurora.org>, <kvalo@...eaurora.org>,
        <linux-wireless@...r.kernel.org>
Subject: Re: [RFC net-next 2/4] ethtool: extend coalesce setting uAPI with
 CQE mode

On Wed, 26 May 2021 17:27:40 +0800 Huazhong Tan 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 'ETHTOOL_A_COALESCE_USE_CQE_TX' and
> 'ETHTOOL_A_COALESCE_USE_CQE_RX' attribute and expand struct
> kernel_ethtool_coalesce with use_cqe_mode_tx and use_cqe_mode_rx,
> then these parameters can be accessed by ethtool netlink coalesce
> uAPI.
> 
> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>

> diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
> index 25131df..975394e 100644
> --- a/Documentation/networking/ethtool-netlink.rst
> +++ b/Documentation/networking/ethtool-netlink.rst
> @@ -937,6 +937,8 @@ Kernel response contents:
>    ``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    Tx CQE mode
> +  ``ETHTOOL_A_COALESCE_USE_CQE_RX``	       bool    Rx CQE mode
>    ===========================================  ======  =======================
>  
>  Attributes are only included in reply if their value is not zero or the
> @@ -975,6 +977,8 @@ Request contents:
>    ``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    Tx CQE mode
> +  ``ETHTOOL_A_COALESCE_USE_CQE_RX``	       bool    Rx CQE mode
>    ===========================================  ======  =======================
>  
>  Request is rejected if it attributes declared as unsupported by driver (i.e.

You need to thoroughly document the semantics. Can you point us to
which drivers/devices implement similar modes of operation (if they
exist we need to make sure semantics match)?

> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
> index 1030540..9d0a386 100644
> --- a/include/linux/ethtool.h
> +++ b/include/linux/ethtool.h
> @@ -179,6 +179,8 @@ __ethtool_get_link_ksettings(struct net_device *dev,
>  
>  struct kernel_ethtool_coalesce {
>  	struct ethtool_coalesce	base;
> +	__u32	use_cqe_mode_tx;
> +	__u32	use_cqe_mode_rx;

No __ in front, this is not a user space structure.
Why not bool or a bitfield?

>  };
>  
>  /**

> @@ -216,6 +223,8 @@ const struct nla_policy ethnl_coalesce_set_policy[] = {
>  	[ETHTOOL_A_COALESCE_TX_USECS_HIGH]	= { .type = NLA_U32 },
>  	[ETHTOOL_A_COALESCE_TX_MAX_FRAMES_HIGH]	= { .type = NLA_U32 },
>  	[ETHTOOL_A_COALESCE_RATE_SAMPLE_INTERVAL] = { .type = NLA_U32 },
> +	[ETHTOOL_A_COALESCE_USE_CQE_MODE_TX]	= { .type = NLA_U8 },
> +	[ETHTOOL_A_COALESCE_USE_CQE_MODE_RX]	= { .type = NLA_U8 },

This needs a policy to make sure values are <= 1.