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

Hari Bathini hbathini at linux.ibm.com
Fri Oct 20 18:50:44 AEDT 2023

On 18/10/23 1:51 pm, Pingfan Liu wrote:
> 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.

I hope so too.

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