On Tue, May 07, 2019 at 11:28:04AM +1000, Suraj Jitindar Singh wrote: > On Mon, 2019-05-06 at 16:15 +1000, David Gibson wrote: > > On Fri, May 03, 2019 at 03:53:05PM +1000, Suraj Jitindar Singh wrote: > > > The Processor Utilisation of Resources Register (PURR) and Scaled > > > Processor Utilisation of Resources Register (SPURR) provide an > > > estimate > > > of the resources used by the thread, present on POWER7 and later > > > processors. > > > > > > Currently the [S]PURR registers simply count at the rate of the > > > timebase. > > > > > > Preserve this behaviour but rework the implementation to store an > > > offset > > > like the timebase rather than doing the calculation manually. Also > > > allow > > > hypervisor write access to the register along with the currently > > > available read access. > > > > > > Signed-off-by: Suraj Jitindar Singh <sjitindarsi...@gmail.com> > > > > Hm. How will this affect migration of the PURR and SPURR? > > So as it turns out, the PURR isn't acutually migrated. We rely on the > fact that the QEMU_CLOCK_VIRTUAL is migrated and that the PURR can > never change value. Since it just counts at the same rate as the time > base we get away with it.
Ah, ok.
> For this to work we will need to add PURR, and VTB for the later patch
> which adds it to the migration stream. I suggest me just migrate by
> value meaning the internal representation can infact change in future
> without breaking migration.
Yes, that sounds good, and we even already have a spot for it in the
sprs array.
At first I was thinking we'd need to fiddle about with adjusting it
afterwards to account for the migration downtime (as we do for tb),
but then I realised that it probably makes more sense *not* to count
the migration downtime against purr and spurr, which makes it even
easier.
>
> What this means is that this patch changing the internal representation
> if fine given migration is broken anyway. When I resend this series
> I'll add the purr and vtb to the migration stream.
Ok, sounds good, therefore:
Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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