Re: [Xen-devel] [RFC V2] xen: interface: introduce pvclk interface

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2016-01-20 at 22:37 +0800, Peng Fan wrote:
>Â
> > Then (also considering the set of commands you propose) what
> > use is the clock to the guest? It can't get events from it, it can't
> > read its current value, all it can is get/set its rate, enable/disable,
> > and prepare/unprepare it. I may be lacking some ARM knowledge
> > here, but all of this looks pretty odd to me.

Perhaps it helps to mention that these are the clocks which drive the
silicon in the device IP (in the "I have a 2GHz processor" sense), rather
than anything to do with time or (s/w visible) events.

On x86 these are not often under OS control, but on ARM it is common for
the network of clocks and associated muxers and dividers to be made
available to the OS in quite a fine grained manner and for
unused/unnecessary clocks to be disabled or under utilised ones to be
scaled to save power etc.

Ian.


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