linux-kernel - Re: [PATCH 09/11] pps: low level IRQ timestamps recording.

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Message-ID: <20091203120130.GD12943@gundam.enneenne.com>
Date:	Thu, 3 Dec 2009 13:01:30 +0100
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Dave Jones <davej@...hat.com>, Sam Ravnborg <sam@...nborg.org>,
	Greg KH <greg@...ah.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 09/11] pps: low level IRQ timestamps recording.

On Wed, Dec 02, 2009 at 04:10:44PM -0800, H. Peter Anvin wrote:
> On 12/02/2009 09:18 AM, Rodolfo Giometti wrote:
> > Add low level IRQ timestamps recording for x86 (32 and 64 bits)
> > platforms and enable UART clients in order to use it.
> > 
> > This improves PPS precision. :)
> 
> It also invokes getnstimeofday on every single interrupt, including ones
> which have absolutely nothing to do with the PPS, and are potentially
> high volume.  getnstimeofday can be a fairly expensive operation,
> especially if the best available clock is away from the CPU, or it
> requires extensive arithmetic in order to normalize the clock value...

I see, that's why I propose my patches to you: in order to have some
feedbacks for better solutions. :)

Can I add a IRQF_TIMESTAMP in order to ask to the system to record irq
timestamps for particular irq lines? The problem is that I cannot set
that flag at irq_register() time but I have to do it later... it can
be a problem?

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
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