[Skiboot] [PATCH v7 18/22] fadump: Add documentation

[Stewart Smith]

Oliver <oohall at gmail.com> writes:
> On Tue, May 28, 2019 at 10:46 PM Vasant Hegde
> <hegdevasant at linux.vnet.ibm.com> wrote:
>>
>> On 05/20/2019 11:50 AM, Oliver wrote:
>> > *snip*
>
>> Are you sure you are counting it properly? I suspect some of these numbers.
>> Either numbers are wrong -OR- we messed up badly.
>>
>> > +---------------------------------+-------+
>> > |            OPAL Call            | Count |
>> > +---------------------------------+-------+
>> > | OPAL_READ_NVRAM                 |  4612 |
>>
>> Why are we doing so many NVRAM calls.
>
> Apparently the kernel reads the whole of NVRAM in 200 byte chunks. The
> default NVRAM size of OpenPower systems seems to be 576KB and 1MB on
> FSP systems so you end up doing a lot of them.

That seems... suboptimal.

Although, from a dumb test of putting a printf in the OPAL code for it,
I just get 3 reads of 16 bytes each and then a lot (~1000) 512 byte reads as
petitboot comes up.

So, I guess, with a 1MB NVRAM on FSP, and including booting to an OS,
~4000 is about right.

Urgh..

Looking at what's actually dictating that size, it seems to be mostly
all in the nvram utility itself, which weirdly wants to just always read
it in 512 byte chunks.

We could plausibly fix that though.


-- 
Stewart Smith
OPAL Architect, IBM.