Re: [Xen-devel] [PATCH 1/2] x86: identifying the boot cpu

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.03.15 at 19:07, <uma.sharma523@xxxxxxxxx> wrote:
> Provide helpers to access the socket and core IDs, resulting from
> identification phase.

Such helpers already exist, as can be seen from the context of the
hunk changing xen/include/asm-x86/processor.h. What you add
are accessors specifically for the boot CPU.

> Initialize socket and core ID to -1 i.e invalid instead of 0. Having
> that field in all elements set to 0 would induce credit2 to think that
> the pCPU have already been initialized, and that all are on socket 0
> in case of credit2 socket scheduler and on core 0 in case of credit2
> core scheduler.

So how would the scheduler initialization work better should it
happen to encounter a -1 here? I.e. how is the change you
describe an improvement? In the end - aiui - you want to make
sure these fields get initialized properly on all CPUs before the
scheduler first looks at them. And if you achieve that, I can't
see how changing the initializers would make any difference. As
a side note - if this was really important, I'm sure you would also
want to add respective initializers for boot_cpu_data. Plus it
would remain to be explained why compute_unit_id wouldn't
also want to be non-zero-initialized.

Assuming this my understanding of the goal of the patch is
correct, then the title still misses the word "earlier" (or some
equivalent) to properly describe what all this is about, and
the description still fails to explicitly state the reason for this
(one can now guess that, I admit).

Jan


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