Re: [Qemu-devel] [RFC 04/17] pseries: Make cpu_update during CAS unconditional

[David Gibson]

On Fri, Nov 04, 2016 at 11:45:43AM +0100, Thomas Huth wrote:
> On 30.10.2016 12:11, David Gibson wrote:
> > spapr_h_cas_compose_response() includes a cpu_update parameter which
> > controls whether it includes updated information on the CPUs in the device
> > tree fragment returned from the ibm,client-architecture-support (CAS) call.
> > 
> > Providing the updated information is essential when CAS has negotiated
> > compatibility options which require different cpu information to be
> > presented to the guest.  However, it should be safe to provide in other
> > cases (it will just override the existing data in the device tree with
> > identical data).  This simplifies the code by removing the parameter and
> > always providing the cpu update information.
> 
> But updating the CPU device tree again and again will also increase the
> QEMU start-up time... Considering that guest start up time is sometimes
> also an issue, do you think that this code simplification really worth
> the effort here?

Given how much it made my brain hurt to try to work the subsequent
changes around that parameter; yes.

If we really have problems with startup time we can revisit this - and
we can probably do better in the context of cleaned up dt building.

-- 
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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