Re: [PATCH v2 2/2] qemu-options.hx: Document hmat-lb and hmat-cache order

[Michal Privoznik <mprivozn@redhat.com>]

On 6/15/20 10:02 AM, Markus Armbruster wrote:
> Michal Privoznik <mprivozn@redhat.com> writes:
> 
>> To simplify internal implementation the hmat-cache parsing code
>> expects hmat-lb to be already parsed. This means, that hmat-lb
>> arguments must come before hmat-cache. Document this restriction
>> so that management applications can follow it.
>>
>> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
>> ---
>>   qemu-options.hx | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index b1a399079a..3fe9e6d6a0 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -319,6 +319,9 @@ SRST
>>       'none/direct(direct-mapped)/complex(complex cache indexing)'. policy
>>       is the write policy. line is the cache Line size in bytes.
>>   
>> +    Please note, that due to internal implementation, '\ ``hmat-cache``\ '
>> +    must be configured only after '\ ``hmat-lb``\ ' option.
>> +
>>       For example, the following options describe 2 NUMA nodes. Node 0 has
>>       2 cpus and a ram, node 1 has only a ram. The processors in node 0
>>       access memory in node 0 with access-latency 5 nanoseconds,
> 
> What happens when we do it wrong?
> 

We error out.

https://lists.nongnu.org/archive/html/qemu-devel/2020-05/msg08409.html

> Can we catch doing it wrong somehow?  I figure that would be much better
> than merely documenting it.
> 

Sure, but that would require some more code (according to Igor's e-mail 
and discussion linked from the linked document). And frankly, to libvirt 
it doesn't matter. For everybody else, let's document it at least and if 
somebody ever writes the missing piece we can remove the restriction 
from the docs.

Michal