Re: [RFC PATCH 2/4] spapr: TCG: Migrate spapr_cpu->prod

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Feb 24, 2022 at 03:58:15PM -0300, Fabiano Rosas wrote:
> I'm seeing some stack traces in the migrated guest going through cede
> and some hangs at the plpar_hcall_norets so let's make sure everything
> related to cede/prod is being migrated just in case.

This is a poor approach in general.  Migration becomes even harder to
maintain than it already is if you don't pare down the set of migrated
data to something minimal and non-redundant.

If you want to migrate prod, you have to give a case for why you
*need* it, not "just in case".

Also, you have to put this in a subsection with a needed function in
order not to break compatibility.

> 
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
> ---
>  hw/ppc/spapr_cpu_core.c         | 1 +
>  include/hw/ppc/spapr_cpu_core.h | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> index ed84713960..efda7730f1 100644
> --- a/hw/ppc/spapr_cpu_core.c
> +++ b/hw/ppc/spapr_cpu_core.c
> @@ -179,6 +179,7 @@ static const VMStateDescription vmstate_spapr_cpu_state = {
>      .version_id = 1,
>      .minimum_version_id = 1,
>      .fields = (VMStateField[]) {
> +        VMSTATE_BOOL(prod, SpaprCpuState),
>          VMSTATE_END_OF_LIST()
>      },
>      .subsections = (const VMStateDescription * []) {
> diff --git a/include/hw/ppc/spapr_cpu_core.h b/include/hw/ppc/spapr_cpu_core.h
> index b560514560..2772689c84 100644
> --- a/include/hw/ppc/spapr_cpu_core.h
> +++ b/include/hw/ppc/spapr_cpu_core.h
> @@ -45,7 +45,7 @@ typedef struct SpaprCpuState {
>      uint64_t vpa_addr;
>      uint64_t slb_shadow_addr, slb_shadow_size;
>      uint64_t dtl_addr, dtl_size;
> -    bool prod; /* not migrated, only used to improve dispatch latencies */
> +    bool prod;
>      struct ICPState *icp;
>      struct XiveTCTX *tctx;
>  

-- 
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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