netdev - Re: [PATCH net-next 2/2] igb: offer a PTP Hardware Clock instead of the timecompare method

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Date:	Tue, 13 Dec 2011 04:28:52 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net,
	Jacob Keller <jacob.e.keller@...el.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	John Ronciak <john.ronciak@...el.com>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH net-next 2/2] igb: offer a PTP Hardware Clock instead of
 the timecompare method

Le mardi 13 décembre 2011 à 04:00 +0100, Richard Cochran a écrit :
> This commit removes the legacy timecompare code from the igb driver and
> offers a tunable PHC instead.
> 
> Signed-off-by: Richard Cochran <richardcochran@...il.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 = OFL_SHIFT_82580;
> +		msb_set = (systim >> 32) & SYSTIMH_MSB_82580;
> +		break;
> +	case e1000_82576:
> +		shift = OFL_SHIFT_82576;
> +		msb_set = (systim >> 32) & SYSTIMH_MSB_82576;
> +		break;
> +	default:
> +		return;
> +	}
> +
> +	spin_lock_irqsave(&adapter->tmreg_lock, flags);
> +
> +	ns = igb_overflow_get(adapter, systim, msb_set, shift);
> +
> +	spin_unlock_irqrestore(&adapter->tmreg_lock, flags);
> +
> +	memset(hwtstamps, 0, sizeof(*hwtstamps));
> +	hwtstamps->hwtstamp = 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 ?



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