netdev - Re: [PATCH net-next v2 1/6] ice: do not busy-wait to read GNSS data

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Date:   Mon, 17 Apr 2023 13:58:21 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Michal Schmidt <mschmidt@...hat.com>
Cc:     intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Karol Kolacinski <karol.kolacinski@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Michal Michalik <michal.michalik@...el.com>,
        Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
        Petr Oros <poros@...hat.com>, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next v2 1/6] ice: do not busy-wait to read GNSS data

On Wed, Apr 12, 2023 at 10:19:24AM +0200, Michal Schmidt wrote:
> The ice-gnss-<dev_name> kernel thread, which reads data from the u-blox
> GNSS module, keep a CPU core almost 100% busy. The main reason is that
> it busy-waits for data to become available.
> 
> A simple improvement would be to replace the "mdelay(10);" in
> ice_gnss_read() with sleeping. A better fix is to not do any waiting
> directly in the function and just requeue this delayed work as needed.
> The advantage is that canceling the work from ice_gnss_exit() becomes
> immediate, rather than taking up to ~2.5 seconds (ICE_MAX_UBX_READ_TRIES
> * 10 ms).
> 
> This lowers the CPU usage of the ice-gnss-<dev_name> thread on my system
> from ~90 % to ~8 %.
> 
> I am not sure if the larger 0.1 s pause after inserting data into the
> gnss subsystem is really necessary, but I'm keeping that as it was.
> 
> Of course, ideally the driver would not have to poll at all, but I don't
> know if the E810 can watch for GNSS data availability over the i2c bus
> by itself and notify the driver.
> 
> Signed-off-by: Michal Schmidt <mschmidt@...hat.com>

Reviewed-by: Simon Horman <simon.horman@...igine.com>