netdev - Re: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of the timecompare method

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Date:	Fri, 23 Mar 2012 07:05:56 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	"Keller, Jacob E" <jacob.e.keller@...el.com>
Cc:	chetan loke <loke.chetan@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"john.stultz@...aro.org" <john.stultz@...aro.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of
 the timecompare method

On Thu, Mar 22, 2012 at 09:59:01PM +0000, Keller, Jacob E wrote:
> 
> This means that readers don't block at all, and as long as the
> readers don't conflict with each other, there is no contention or
> writer starvation. It is possible for readers to 'live' lock, due to
> a large number of write operations. However, the lock is designed
> for few-writers, many readers. Which is what we have.

The readers do conflict with each other simply by reading the
registers E1000_SYSTIML and E1000_SYSTIMH. The locking is needed in
order to make these two reads "atomic."

Thanks,
Richard
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