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Date:   Fri, 14 Sep 2018 16:27:47 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Andy Lutomirski <luto@amacapital.net>
cc:     LKML <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>, x86@kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Matt Rickard <matt@softrans.com.au>,
        Stephen Boyd <sboyd@kernel.org>,
        John Stultz <john.stultz@linaro.org>,
        Florian Weimer <fweimer@redhat.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        devel@linuxdriverproject.org,
        virtualization@lists.linux-foundation.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>, Juergen Gross <jgross@suse.com>
Subject: Re: [patch 11/11] x66/vdso: Add CLOCK_TAI support
In-Reply-To: <ABB53D42-2A06-41B9-8A8C-40B39CD0289D@amacapital.net>
Message-ID: <alpine.DEB.2.21.1809141625040.10480@nanos.tec.linutronix.de>
References: <20180914125006.349747096@linutronix.de> <20180914125119.081037164@linutronix.de> <ABB53D42-2A06-41B9-8A8C-40B39CD0289D@amacapital.net>
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On Fri, 14 Sep 2018, Andy Lutomirski wrote:
> > On Sep 14, 2018, at 5:50 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > 
> > With the storage array in place it's now trivial to support CLOCK_TAI in
> > the vdso. Instead of extending the array to accomodate CLOCK_TAI, make use
> > of the fact that:
> > 
> > - CLOCK ids are set in stone
> > - CLOCK_THREAD_CPUTIME is never going to be supported in the VDSO so
> >   the array slot 3 is unused
> > - CLOCK_TAI is id 11 which results in 3 when masked with 0x3
> > 
> > Add the mask to the basetime array lookup and set up the CLOCK_TAI base
> > time in update_vsyscall().
> 
> That’s... horrible. In an amazing way. Can you add BUILD_BUG_ON somewhere
> to assert that this actually works?

Sure, but changing any of the clock ids will cause more wreckage than that.

Thanks,

	tglx
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