netdev - Re: [RFC V2 net-next 1/3] ethtool: extend coalesce setting uAPI with CQE mode

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Message-ID: <20210531220917.3df91899@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Mon, 31 May 2021 22:09:17 -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 V2 net-next 1/3] ethtool: extend coalesce setting uAPI
 with CQE mode

On Mon, 31 May 2021 09:24:01 +0800 Huazhong Tan wrote:
> >> @@ -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    timer reset in CQE, Tx
> >> +  ``ETHTOOL_A_COALESCE_USE_CQE_RX``	       bool    timer reset in CQE, Rx
> >>     ===========================================  ======  =======================
> >>   
> >>   Request is rejected if it attributes declared as unsupported by driver (i.e.  
> > Did you provide the theory of operation for CQE vs EQE mode somewhere,
> > as I requested?  
> 
> 
> the definition of enum dim_cq_period_mode in include/linux/dim.h has
> 
> below comment:
> 
> /**
>   * enum dim_cq_period_mode - Modes for CQ period count
>   *
>   * @DIM_CQ_PERIOD_MODE_START_FROM_EQE: Start counting from EQE
>   * @DIM_CQ_PERIOD_MODE_START_FROM_CQE: Start counting from CQE (implies 
> timer reset)
>   * @DIM_CQ_PERIOD_NUM_MODES: Number of modes
>   */
> 
> 
> is this comment suitable? and add reference in 
> Documentation/networking/ethtool-netlink.rst to
> 
> the comment in dim.h.

DIM is kernel internals we need user facing, meaningful documentation.
I'm not 100% clea on what the exact difference is.

If the difference is whether timer is restarted on new packet arrival
or not - why mention CQE at all and not just call the configuration
knob "restart timer on new packet arrival"?