netdev - Re: [PATCH net-next] bnxt_en: optimize gettimex64

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Message-ID: <CACKFLi=eTekiVDLzaJ4dYJ5EG-wRS7-sJdYF=aDCW2jONVCXCw@mail.gmail.com>
Date: Tue, 12 Nov 2024 10:05:50 -0800
From: Michael Chan <michael.chan@...adcom.com>
To: Vadim Fedorenko <vadfed@...a.com>
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, Pavan Chebbi <pavan.chebbi@...adcom.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, Paolo Abeni <pabeni@...hat.com>, 
	Jakub Kicinski <kuba@...nel.org>, Richard Cochran <richardcochran@...il.com>, netdev@...r.kernel.org, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net-next] bnxt_en: optimize gettimex64

On Tue, Nov 12, 2024 at 3:06 AM Vadim Fedorenko <vadfed@...a.com> wrote:
>
> Current implementation of gettimex64() makes at least 3 PCIe reads to
> get current PHC time. It takes at least 2.2us to get this value back to
> userspace. At the same time there is cached value of upper bits of PHC
> available for packet timestamps already. This patch reuses cached value
> to speed up reading of PHC time.
>
> Signed-off-by: Vadim Fedorenko <vadfed@...a.com>

> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
> index 91e7e08fabb1..8764ce412f7b 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c

> @@ -162,13 +184,19 @@ static int bnxt_ptp_gettimex(struct ptp_clock_info *ptp_info,
>  {
>         struct bnxt_ptp_cfg *ptp = container_of(ptp_info, struct bnxt_ptp_cfg,
>                                                 ptp_info);
> -       u64 ns, cycles;
> +       u64 ns, cycles, time;
> +       u32 low;
>         int rc;
>
> -       rc = bnxt_refclk_read(ptp->bp, sts, &cycles);
> +       rc = bnxt_refclk_read_low(ptp->bp, sts, &low);
>         if (rc)
>                 return rc;
>
> +       time = (u64)READ_ONCE(ptp->old_time) << BNXT_HI_TIMER_SHIFT;
> +       cycles = (time & BNXT_HI_TIMER_MASK) | low;
> +       if (low < (time & BNXT_LO_TIMER_MASK))
> +               cycles += BNXT_LO_TIMER_MASK + 1;
> +

Looks good to me.  I think this logic here to get the upper bits and
check for overflow is identical to the RX timestamp logic.  It may be
worthwhile to have a common helper function to do this.  Other than
that,

Reviewed-by: Michael Chan <michael.chan@...adocm.com>

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