linux-kernel - Re: [PATCH v2 1/7] timekeeping: introduce __current_kernel

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Message-ID: <alpine.DEB.2.02.1511101429100.5676@kaball.uk.xensource.com>
Date:	Tue, 10 Nov 2015 14:34:13 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<xen-devel@...ts.xensource.com>,
	<linux-arm-kernel@...ts.infradead.org>, <Ian.Campbell@...rix.com>,
	<linux-kernel@...r.kernel.org>, <arnd@...db.de>,
	<john.stultz@...aro.org>, <tglx@...utronix.de>, <mingo@...nel.org>
Subject: Re: [PATCH v2 1/7] timekeeping: introduce __current_kernel_time64

On Tue, 10 Nov 2015, Peter Zijlstra wrote:
> On Tue, Nov 10, 2015 at 11:57:49AM +0000, Stefano Stabellini wrote:
> > __current_kernel_time64 returns a struct timespec64, without taking the
> > xtime lock. Mirrors __current_kernel_time/current_kernel_time.
> 
> It always helps if you include a reason why you want a patch.

You are right, sorry.

I need to get the current_kernel_time from a pvclock_gtod callback
function, which cannot take the lock again.

On x86 we are just calling __current_kernel_time() (see
arch/x86/xen/time.c:xen_pvclock_gtod_notify). I was introducing the same
functionality on ARM, when the maintainers pointed out that it might be
better to use struct timespec64 and related functions for
future-proofness. To do that I need a version of __current_kernel_time
which returns a struct timespec64.
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