netdev - Re: [Intel-wired-lan] [PATCH 249/249] net:ethernet:intel:igb_main.c: Add Throttling disable option in order to decrease latency usually required by RT applications.

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Date:   Wed, 7 Sep 2016 14:49:39 +0000
From:   "Duyck, Alexander H" <alexander.h.duyck@...el.com>
To:     "amiry@...es.com" <amiry@...es.com>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "shannon.nelson@...el.com" <shannon.nelson@...el.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "matthew.vick@...el.com" <matthew.vick@...el.com>,
        "john.ronciak@...el.com" <john.ronciak@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH 249/249]
 net:ethernet:intel:igb_main.c: Add Throttling disable option in order to
 decrease latency usually required by RT applications.

On Tue, 2016-09-06 at 14:46 +0000, Amir Yihie wrote:
> From e433f5bedd49a65b7337d025f3f204f0f21ad5e5 Mon Sep 17 00:00:00
> 2001
> From: amiry <amiry@...es.com>
> Date: Tue, 6 Sep 2016 14:58:38 +0300
> Subject: [PATCH 249/249] net:ethernet:intel:igb_main.c: Add
> Throttling disable
>  option in order to decrease latency usually required by RT
> applications.
> 
> Add an option to Disable Throttling algorithm , which will result
> with minimum latency on received frames .
> mainly targets for RT application that look for low larceny and less
> cares about throughput .
> How to use :
> On insmod , add parameter : InterruptThrottleRate=0
> 
> This patch is currently against a linux 4.1.27-rt31 kernel.
> 
> Signed-off-by: Amir Yihie <amiry@...es.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
> b/drivers/net/ethernet/intel/igb/igb_main.c
> index 7dfbcde..9480850 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -251,6 +251,14 @@ static int debug = -1;
>  module_param(debug, int, 0);
>  MODULE_PARM_DESC(debug, "Debug level (0=none,...,16=all)");
>  
> +/* Interrupt Throttle Rate (interrupts/sec)
> + *
> + * Valid Range: 0=off, 3=dynamic conservative
> + */
> +static int InterruptThrottleRate = 3;
> +module_param(InterruptThrottleRate, int, 0);
> +MODULE_PARM_DESC(InterruptThrottleRate, "InterruptThrottleRate
> (0=off, 3=dynamic conservative)");
> +

This is creating redundant functionality.  The same can be done via the
ethtool command "ethtool -C <iface> rx-usecs 0".  Is there some reason
why you couldn't use ethtool?

>  struct igb_reg_info {
>         u32 ofs;
>         char *name;
> @@ -2966,6 +2974,9 @@ static int igb_sw_init(struct igb_adapter
> *adapter)
>         adapter->rx_itr_setting = IGB_DEFAULT_ITR;
>         adapter->tx_itr_setting = IGB_DEFAULT_ITR;
>  
> +       if (InterruptThrottleRate == 0)
> +               adapter->rx_itr_setting = InterruptThrottleRate;
> +
>         /* set default work limits */
>         adapter->tx_work_limit = IGB_DEFAULT_TX_WORK;

If you are going to use InterruptThrottleRate you might as well use it
fully instead of making it a boolean value with 0 having one meaning
and the default of 3 being another.

Thanks.

- Alex