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

[Fabiano Rosas]

David Gibson <david@gibson.dropbear.id.au> writes:

> 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".

Ah yes, I'm not actually trying to merge stuff without a good
explanation. I haven't even delineated the problem properly. But I know
little about migration so I need to do some probing, bear with me
please.

> 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;
>>