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

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Message-ID: <20120324065147.GB2201@netboy.at.omicron.at>
Date:	Sat, 24 Mar 2012 07:51:49 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	chetan loke <loke.chetan@...il.com>
Cc:	"Keller, Jacob E" <jacob.e.keller@...el.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 Fri, Mar 23, 2012 at 03:39:08PM -0400, chetan loke wrote:
> 
> So, how is it working today? Because we could have tx and rx
> completions on different CPUs. Is it not possible to have the
> following race today - between timecompare_update->timecompare_offset
> -> timecounter_readdelta of say Rx and timecounter_cyc2time from Tx?

I works (in the igb) because of the spinlock. You know, that thing
that you are so against using.

> So yes, rate limiting ioctls seems like a good idea.

No, that is a terrible idea.
 
> How about rate limiting at the PHC class driver level? And then it
> will work across the board for all the adapters at the device level.

No, don't go there. Enough bikeshedding already. If you have a serious
performance issue, please post a test case, and we will look for a
solution.

Thanks,
Richard


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