[PATCHv9 2/2] powerpc/setup: Loosen the mapping between cpu logical id and its seq in dt

[Pingfan Liu]

On Tue, Oct 17, 2023 at 6:39 PM Hari Bathini <hbathini at linux.ibm.com> wrote:
>
>
>
> On 17/10/23 7:58 am, Pingfan Liu wrote:
> > *** Idea ***
> > For kexec -p, the boot cpu can be not the cpu0, this causes the problem
> > of allocating memory for paca_ptrs[]. However, in theory, there is no
> > requirement to assign cpu's logical id as its present sequence in the
> > device tree. But there is something like cpu_first_thread_sibling(),
> > which makes assumption on the mapping inside a core. Hence partially
> > loosening the mapping, i.e. unbind the mapping of core while keep the
> > mapping inside a core.
> >
> > *** Implement ***
> > At this early stage, there are plenty of memory to utilize. Hence, this
> > patch allocates interim memory to link the cpu info on a list, then
> > reorder cpus by changing the list head. As a result, there is a rotate
> > shift between the sequence number in dt and the cpu logical number.
> >
> > *** Result ***
> > After this patch, a boot-cpu's logical id will always be mapped into the
> > range [0,threads_per_core).
> >
> > Besides this, at this phase, all threads in the boot core are forced to
> > be onlined. This restriction will be lifted in a later patch with
> > extra effort.
> >
> > Signed-off-by: Pingfan Liu <piliu at redhat.com>
> > Cc: Michael Ellerman <mpe at ellerman.id.au>
> > Cc: Nicholas Piggin <npiggin at gmail.com>
> > Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> > Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
> > Cc: Wen Xiong <wenxiong at us.ibm.com>
> > Cc: Baoquan He <bhe at redhat.com>
> > Cc: Ming Lei <ming.lei at redhat.com>
> > Cc: Sourabh Jain <sourabhjain at linux.ibm.com>
> > Cc: Hari Bathini <hbathini at linux.ibm.com>
> > Cc: kexec at lists.infradead.org
> > To: linuxppc-dev at lists.ozlabs.org
>
> Thanks for working on this, Pingfan.
> Looks good to me.
>
> Acked-by: Hari Bathini <hbathini at linux.ibm.com>
>

Thank you for kindly reviewing. I hope that after all these years, we
have accomplished the objective.

Best Regards,

Pingfan