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Re: RADclock on Xen (was Re: [Xen-devel] [PATCH] time-xen : Reset monoto

To: Darryl Veitch <dveitch@xxxxxxxxxxxxxx>
Subject: Re: RADclock on Xen (was Re: [Xen-devel] [PATCH] time-xen : Reset monotonic time when sync up time from dom0 to domU)
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 15 Oct 2010 16:21:05 -0700
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxx>, Shunli Yi <syi@xxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Saipu Liu <saliu@xxxxxxxxxxxx>, Hang Du <hdu@xxxxxxxxxxxx>, Timothy Broomhead <tim@xxxxxxxxxxxxxxx>, Julien Ridoux <jridoux@xxxxxxxxxxxxxx>
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 On 10/15/2010 05:10 AM, Darryl Veitch wrote:
> Hi Tim,
> good to hear from you.  Dom0 will need the usual RADclock patches
> which now integrate the Xen support. These supply two main things:  
> i)  kernel level raw timestamping (ie reading of the chosen counter)
> of packet arrivals and departures in `good but safe' locations and an
> ability to pass those timestamps up (works transparently with pcap,
> and doesn't affect its normal operation)

Are you trying to get these changes into mainline Linux?

> ii)  the ability to access the raw counter of choice from both kernel
> and user context

The kernel already has this info, and I have patches for mapping it into
userspace.  Or would a syscall suffice?

> In the Xen context, the choice of counter will end up being Xen
> Clocksource which is already accessible to guests as is already a
> suitable counter of the right size (64-bit).
> Take a look at the RADclock downloads
> <http://www.cubinlab.ee.unimelb.edu.au/radclock/download.php> page.
> There have been a number of changes recently in particular in the
> integration of the Xen support so I will direct you to Julien Ridoux
> for finer-grained answers as he and Tim Broomhead actually wrote the
> code. 
> We'll be quizzing you shortly about our needs to make this work under
> HV using that way to access the Xenstore you mentioned, and we'd like
> to talk to you about how to improve packet timestamping under Dom0. 



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