From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: vsyscall support in 2.6.{32,33}
Date: Tue, 21 Sep 2010 10:31:55 -0700
Message-ID: <4C98EC0B.3090005@goop.org>
References: <4C98A9CD.1090900@redhat.com> <20100921130910.GQ2804@reaktio.net>
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To: =?ISO-8859-1?Q?Pasi_K=E4rkk=E4inen?= <pasik@iki.fi>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Drew Jones <drjones@redhat.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

 On 09/21/2010 06:09 AM, Pasi K=E4rkk=E4inen wrote:
> On Tue, Sep 21, 2010 at 02:49:17PM +0200, Paolo Bonzini wrote:
>> Besides the obvious fact that the required hypercall is not supported =
by =20
>> any released hypervisor, is there any other reason why the xen vsyscal=
l =20
>> code is not in the pvops/stable-2.6.{32,33}.x branches?
>>
>> Thanks!
>>
> I guess Jeremy didn't remember to merge it yet? :)
> Or is there some problem with it?
>

The main problem is that I'm not sure that the Xen clock algorithm can
give strict enough monotonicity for usermode use (ie, can't meet the
expected behaviour of clock_gettime()), and its not at all clear how to
fix it.  I could prevent non-monotonicity within one process, but not
between processes.

    J