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

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Date:	Wed, 21 Mar 2012 17:09:06 +0000
From:	"Keller, Jacob E" <jacob.e.keller@...el.com>
To:	Richard Cochran <richardcochran@...il.com>,
	chetan loke <loke.chetan@...il.com>
CC:	"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

> -----Original Message-----
> From: Richard Cochran [mailto:richardcochran@...il.com]
> Sent: Wednesday, March 21, 2012 10:00 AM
> To: chetan loke
> Cc: netdev@...r.kernel.org; e1000-devel@...ts.sourceforge.net; Keller, Jacob
> E; Kirsher, Jeffrey T; Ronciak, John; john.stultz@...aro.org;
> tglx@...utronix.de
> Subject: Re: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of the
> timecompare method
> 
> Can you please explain how using a seqlock could help here?
> 
> Thanks,
> Richard

My understanding of the seqlock, is that it prevents starvation of the hwtstamp calls in the rx and tx routines if/when a user hammers the gettime ioctl due to bad software design where 100+ apps are wanting direct access to the PHC.

- Jake
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