netdev - Re: [PATCH net-next v2 2/7] ice: Remove gettime HW semaphore

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Date:   Tue, 22 Nov 2022 14:36:27 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Tony Nguyen <anthony.l.nguyen@...el.com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, Karol Kolacinski <karol.kolacinski@...el.com>,
        netdev@...r.kernel.org, Gurucharan G <gurucharanx.g@...el.com>
Subject: Re: [PATCH net-next v2 2/7] ice: Remove gettime HW semaphore

On Tue, Nov 22, 2022 at 02:10:42PM -0800, Tony Nguyen wrote:
> From: Karol Kolacinski <karol.kolacinski@...el.com>
> 
> Reading the time should not block other accesses to the PTP hardware.
> There isn't a significant risk of reading bad values while another
> thread is modifying the clock. Removing the hardware lock around the
> gettime allows multiple application threads to read the clock time with
> less contention.

NAK

Correctness comes before performance.

Thanks,
Richard


> 
> Signed-off-by: Karol Kolacinski <karol.kolacinski@...el.com>
> Tested-by: Gurucharan G <gurucharanx.g@...el.com> (A Contingent worker at Intel)
> Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_ptp.c | 31 +++---------------------
>  1 file changed, 3 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.c b/drivers/net/ethernet/intel/ice/ice_ptp.c
> index 5cf198a33e26..d1bab1876249 100644
> --- a/drivers/net/ethernet/intel/ice/ice_ptp.c
> +++ b/drivers/net/ethernet/intel/ice/ice_ptp.c
> @@ -979,26 +979,6 @@ static void ice_ptp_reset_cached_phctime(struct ice_pf *pf)
>  	ice_ptp_flush_tx_tracker(pf, &pf->ptp.port.tx);
>  }
>  
> -/**
> - * ice_ptp_read_time - Read the time from the device
> - * @pf: Board private structure
> - * @ts: timespec structure to hold the current time value
> - * @sts: Optional parameter for holding a pair of system timestamps from
> - *       the system clock. Will be ignored if NULL is given.
> - *
> - * This function reads the source clock registers and stores them in a timespec.
> - * However, since the registers are 64 bits of nanoseconds, we must convert the
> - * result to a timespec before we can return.
> - */
> -static void
> -ice_ptp_read_time(struct ice_pf *pf, struct timespec64 *ts,
> -		  struct ptp_system_timestamp *sts)
> -{
> -	u64 time_ns = ice_ptp_read_src_clk_reg(pf, sts);
> -
> -	*ts = ns_to_timespec64(time_ns);
> -}
> -
>  /**
>   * ice_ptp_write_init - Set PHC time to provided value
>   * @pf: Board private structure
> @@ -1789,15 +1769,10 @@ ice_ptp_gettimex64(struct ptp_clock_info *info, struct timespec64 *ts,
>  		   struct ptp_system_timestamp *sts)
>  {
>  	struct ice_pf *pf = ptp_info_to_pf(info);
> -	struct ice_hw *hw = &pf->hw;
> +	u64 time_ns;
>  
> -	if (!ice_ptp_lock(hw)) {
> -		dev_err(ice_pf_to_dev(pf), "PTP failed to get time\n");
> -		return -EBUSY;
> -	}
> -
> -	ice_ptp_read_time(pf, ts, sts);
> -	ice_ptp_unlock(hw);
> +	time_ns = ice_ptp_read_src_clk_reg(pf, sts);
> +	*ts = ns_to_timespec64(time_ns);
>  
>  	return 0;
>  }
> -- 
> 2.35.1
>