netdev - Re: [PATCH iwl-net v5] igc: Expose tx-usecs coalesce setting to user

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Date: Sun, 10 Sep 2023 16:24:16 +0200
From: Simon Horman <horms@...nel.org>
To: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@...el.com>
Cc: intel-wired-lan@...osl.org, sasha.neftin@...el.com, bcreeley@....com,
	davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
	edumazet@...gle.com, netdev@...r.kernel.org,
	naamax.meir@...ux.intel.com, anthony.l.nguyen@...el.com,
	husainizulkifli@...il.com
Subject: Re: [PATCH iwl-net v5] igc: Expose tx-usecs coalesce setting to user

On Fri, Sep 08, 2023 at 04:17:34PM +0800, Muhammad Husaini Zulkifli wrote:
> When users attempt to obtain the coalesce setting using the
> ethtool command, current code always returns 0 for tx-usecs.
> This is because I225/6 always uses a queue pair setting, hence
> tx_coalesce_usecs does not return a value during the
> igc_ethtool_get_coalesce() callback process. The pair queue
> condition checking in igc_ethtool_get_coalesce() is removed by
> this patch so that the user gets information of the value of tx-usecs.
> 
> Even if i225/6 is using queue pair setting, there is no harm in
> notifying the user of the tx-usecs. The implementation of the current
> code may have previously been a copy of the legacy code i210.
> Since I225 has the queue pair setting enabled, tx-usecs will always adhere
> to the user-set rx-usecs value. An error message will appear when the user
> attempts to set the tx-usecs value for the input parameters because,
> by default, they should only set the rx-usecs value.

Hi Muhammad,

Most likely I'm misunderstanding things. And even if that is not the
case perhaps this is as good as it gets. But my reading is that
an error will not be raised if a user provides an input value for
tx-usecs that matches the current value of tx-usecs, even if a different
value is provided for rx-usecs (which will also be applied to tx-usecs).

e.g. (untested!)

  # ethool -c <interface>
  ...
  rx-usecs: 3
  ...
  tx-usecs: 3
  ...

  # ethool -C <interface> tx-usecs 3 rx-usecs 4

  # ethool -c <interface>
  ...
  rx-usecs: 4
  ...
  tx-usecs: 4
  ...

...