On Tue, Oct 17, 2023 at 6:39 PM Hari Bathini [off-list ref] wrote:

On 17/10/23 7:58 am, Pingfan Liu wrote:

quoted

*** 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 <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <redacted>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Wen Xiong <redacted>
Cc: Baoquan He <bhe@redhat.com>
Cc: Ming Lei <redacted>
Cc: Sourabh Jain <redacted>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: kexec@lists.infradead.org
To: linuxppc-dev@lists.ozlabs.org

Thanks for working on this, Pingfan.
Looks good to me.

Acked-by: Hari Bathini <hbathini@linux.ibm.com>

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

Best Regards,

Pingfan