netdev - RE: [Intel-wired-lan] [PATCH iwl-next v12 08/14] iavf: periodically cache PHC time

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Message-ID: <SJ0PR11MB5865227E501F005A08B0FC578F512@SJ0PR11MB5865.namprd11.prod.outlook.com>
Date: Mon, 4 Nov 2024 11:01:35 +0000
From: "Romanowski, Rafal" <rafal.romanowski@...el.com>
To: "Polchlopek, Mateusz" <mateusz.polchlopek@...el.com>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "Keller, Jacob E"
	<jacob.e.keller@...el.com>, "Drewek, Wojciech" <wojciech.drewek@...el.com>,
	Simon Horman <horms@...nel.org>, "Polchlopek, Mateusz"
	<mateusz.polchlopek@...el.com>
Subject: RE: [Intel-wired-lan] [PATCH iwl-next v12 08/14] iavf: periodically
 cache PHC time

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of
> Mateusz Polchlopek
> Sent: Tuesday, October 22, 2024 1:41 PM
> To: intel-wired-lan@...ts.osuosl.org
> Cc: netdev@...r.kernel.org; Keller, Jacob E <jacob.e.keller@...el.com>; Drewek,
> Wojciech <wojciech.drewek@...el.com>; Simon Horman <horms@...nel.org>;
> Polchlopek, Mateusz <mateusz.polchlopek@...el.com>
> Subject: [Intel-wired-lan] [PATCH iwl-next v12 08/14] iavf: periodically cache PHC
> time
> 
> From: Jacob Keller <jacob.e.keller@...el.com>
> 
> The Rx timestamps reported by hardware may only have 32 bits of storage for
> nanosecond time. These timestamps cannot be directly reported to the Linux
> stack, as it expects 64bits of time.
> 
> To handle this, the timestamps must be extended using an algorithm that
> calculates the corrected 64bit timestamp by comparison between the PHC time
> and the timestamp. This algorithm requires the PHC time to be captured within
> ~2 seconds of when the timestamp was captured.
> 
> Instead of trying to read the PHC time in the Rx hotpath, the algorithm relies on a
> cached value that is periodically updated.
> 
> Keep this cached time up to date by using the PTP .do_aux_work kthread
> function.
> 
> The iavf_ptp_do_aux_work will reschedule itself about twice a second, and will
> check whether or not the cached PTP time needs to be updated.
> If so, it issues a VIRTCHNL_OP_1588_PTP_GET_TIME to request the time from
> the PF. The jitter and latency involved with this command aren't important,
> because the cached time just needs to be kept up to date within about ~2
> seconds.
> 
> Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
> Reviewed-by: Wojciech Drewek <wojciech.drewek@...el.com>
> Reviewed-by: Simon Horman <horms@...nel.org>
> Co-developed-by: Mateusz Polchlopek <mateusz.polchlopek@...el.com>
> Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@...el.com>
> ---


Tested-by: Rafal Romanowski <rafal.romanowski@...el.com>