> -----Original Message-----
> From: Kitszel, Przemyslaw <przemyslaw.kits...@intel.com>
> Sent: Thursday, April 25, 2024 3:52 AM
> To: Keller, Jacob E <jacob.e.kel...@intel.com>; Polchlopek, Mateusz
> <mateusz.polchlo...@intel.com>; Rahul Rameshbabu
> <rrameshb...@nvidia.com>
> Cc: intel-wired-...@lists.osuosl.org; net...@vger.kernel.org;
> ho...@kernel.org;
> Nguyen, Anthony L <anthony.l.ngu...@intel.com>; Drewek, Wojciech
> <wojciech.dre...@intel.com>
> Subject: Re: [Intel-wired-lan] [PATCH iwl-next v5 08/12] iavf: periodically
> cache
> PHC time
>
> On 4/25/24 00:03, Keller, Jacob E wrote:
> >
> >
> >> -----Original Message-----
> >> From: Polchlopek, Mateusz <mateusz.polchlo...@intel.com>
> >> Sent: Monday, April 22, 2024 2:23 AM
> >> To: Rahul Rameshbabu <rrameshb...@nvidia.com>
> >> Cc: intel-wired-...@lists.osuosl.org; net...@vger.kernel.org;
> ho...@kernel.org;
> >> Nguyen, Anthony L <anthony.l.ngu...@intel.com>; Keller, Jacob E
> >> <jacob.e.kel...@intel.com>; Drewek, Wojciech <wojciech.dre...@intel.com>
> >> Subject: Re: [Intel-wired-lan] [PATCH iwl-next v5 08/12] iavf:
> >> periodically cache
> >> PHC time
> >>
> >>
> >>
> >> On 4/18/2024 9:51 PM, Rahul Rameshbabu wrote:
> >>> On Thu, 18 Apr, 2024 01:24:56 -0400 Mateusz Polchlopek
> >> <mateusz.polchlo...@intel.com> wrote:
> >>>> From: Jacob Keller <jacob.e.kel...@intel.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.
> >>>
> >>> Seems reasonable.
> >>>
> >>>>
> >>>> 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.
> >>>>
> >>>> Reviewed-by: Wojciech Drewek <wojciech.dre...@intel.com>
> >>>> Signed-off-by: Jacob Keller <jacob.e.kel...@intel.com>
> >>>> Co-developed-by: Mateusz Polchlopek <mateusz.polchlo...@intel.com>
> >>>> Signed-off-by: Mateusz Polchlopek <mateusz.polchlo...@intel.com>
> >>>> ---
> >>>> drivers/net/ethernet/intel/iavf/iavf_ptp.c | 52
> ++++++++++++++++++++++
> >>>> drivers/net/ethernet/intel/iavf/iavf_ptp.h | 1 +
> >>>> 2 files changed, 53 insertions(+)
> >>>>
> >>>> diff --git a/drivers/net/ethernet/intel/iavf/iavf_ptp.c
> >> b/drivers/net/ethernet/intel/iavf/iavf_ptp.c
> >>> <snip>
> >>>> +/**
> >>>> + * iavf_ptp_do_aux_work - Perform periodic work required for PTP support
> >>>> + * @ptp: PTP clock info structure
> >>>> + *
> >>>> + * Handler to take care of periodic work required for PTP operation.
> >>>> This
> >>>> + * includes the following tasks:
> >>>> + *
> >>>> + * 1) updating cached_phc_time
> >>>> + *
> >>>> + * cached_phc_time is used by the Tx and Rx timestamp flows in
> >>>> order to
> >>>> + * perform timestamp extension, by carefully comparing the
> >>>> timestamp
> >>>> + * 32bit nanosecond timestamps and determining the corrected 64bit
> >>>> + * timestamp value to report to userspace. This algorithm only
> >>>> works if
> >>>> + * the cached_phc_time is within ~1 second of the Tx or Rx
> >>>> timestamp
> >>>> + * event. This task periodically reads the PHC time and stores it,
> >>>> to
> >>>> + * ensure that timestamp extension operates correctly.
> >>>> + *
> >>>> + * Returns: time in jiffies until the periodic task should be
> >>>> re-scheduled.
> >>>> + */
> >>>> +long iavf_ptp_do_aux_work(struct ptp_clock_info *ptp)
> >>>> +{
> >>>> + struct iavf_adapter *adapter = clock_to_adapter(ptp);
> >>>> +
> >>>> + iavf_ptp_cache_phc_time(adapter);
> >>>> +
> >>>> + /* Check work about twice a second */
> >>>> + return msecs_to_jiffies(500);
> >>>
> >>> HZ / 2 might be more intuitive?
> >>>
> >
> > I've always found it more intuitive to think in terms of msecs myself, but
> > HZ / 2 is
> ok if other folks agree.
>
> HZ/2 or HZ/3 as a timer period could be understood without thinking, but
> the same stands for 400ms. Problems starts when one thinks about it ;)
>
> For me HZ, which could be both literally and colloquially understood as
> "per second" should not mean 1000ms (just evaluate to).
> 2Hz is a frequency with half second period, but 2*HZ evaluates to 2000ms
> which is 4 times more :/
>
That’s part of why I switched ice over from using HZ generally to using
jiffies_to_msec in a lot of cases. It really depends on what you personally
find intuitive. Those used to seeing and reading HZ may find it easier.
Thanks,
Jake
>
> >
> > Thanks,
> > Jake
> >
