linux-kernel - Re: [PATCH 2/2] x86/vdso: Add VCLOCK

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Message-ID: <alpine.DEB.2.20.1702101326520.4036@nanos>
Date:   Fri, 10 Feb 2017 13:28:25 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
cc:     Stephen Hemminger <sthemmin@...rosoft.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read
 method

On Fri, 10 Feb 2017, Vitaly Kuznetsov wrote:

> Stephen Hemminger <sthemmin@...rosoft.com> writes:
> 
> > Why not use existing seqlock's?
> >
> 
> To be honest I don't quite understand how we could use it -- the
> sequence locking here is done against the page updated by the
> hypersior, we're not creating new structures (so I don't understand how
> we could use struct seqcount which we don't have) but I may be
> misunderstanding something.

You can't use seqlock, but you might be able to use seqcount. Though I
doubt it given the 0 check ....

Thanks,

	tglx