From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next 2/2] igb: offer a PTP Hardware Clock instead of
 the timecompare method
Date: Tue, 13 Dec 2011 04:28:52 +0100
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References: <cover.1323744724.git.richardcochran@gmail.com>
	 <388385c50909f63bff239894c60dbb00abc65c93.1323744725.git.richardcochran@gmail.com>
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Cc: netdev@vger.kernel.org, e1000-devel@lists.sourceforge.net,
	Jacob Keller <jacob.e.keller@intel.com>,
	Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
	John Ronciak <john.ronciak@intel.com>,
	John Stultz <john.stultz@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>
To: Richard Cochran <richardcochran@gmail.com>
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Le mardi 13 d=C3=A9cembre 2011 =C3=A0 04:00 +0100, Richard Cochran a =C3=
=A9crit :
> This commit removes the legacy timecompare code from the igb driver a=
nd
> offers a tunable PHC instead.
>=20
> Signed-off-by: Richard Cochran <richardcochran@gmail.com>
> ---

> +void igb_systim_to_hwtstamp(struct igb_adapter *adapter,
> +			    struct skb_shared_hwtstamps *hwtstamps,
> +			    u64 systim)
> +{
> +	u64 ns;
> +	unsigned long flags;
> +	unsigned int shift;
> +	int msb_set;
> +
> +	switch (adapter->hw.mac.type) {
> +	case e1000_i350:
> +	case e1000_82580:
> +		shift =3D OFL_SHIFT_82580;
> +		msb_set =3D (systim >> 32) & SYSTIMH_MSB_82580;
> +		break;
> +	case e1000_82576:
> +		shift =3D OFL_SHIFT_82576;
> +		msb_set =3D (systim >> 32) & SYSTIMH_MSB_82576;
> +		break;
> +	default:
> +		return;
> +	}
> +
> +	spin_lock_irqsave(&adapter->tmreg_lock, flags);
> +
> +	ns =3D igb_overflow_get(adapter, systim, msb_set, shift);
> +
> +	spin_unlock_irqrestore(&adapter->tmreg_lock, flags);
> +
> +	memset(hwtstamps, 0, sizeof(*hwtstamps));
> +	hwtstamps->hwtstamp =3D ns_to_ktime(ns);
> +}

Adding a (shared) spinlock on a multiqueue device is source of extra
delay (because of extra cache line trafic), I guess.

It seems current code doesnt need a spinlock, maybe it was a bug ?