On Tue, Oct 10, 2023 at 01:56:13PM +0530, Hari Bathini wrote:
>
>
> On 09/10/23 5:00 pm, Pingfan Liu wrote:
> > If the boot_cpuid is smaller than nr_cpus, it requires extra effort to
> > ensure the boot_cpu is in cpu_present_mask. This can be achieved by
> > reserving the last quota for the boot cpu.
> >
> > Note: the restriction on nr_cpus will be lifted with more effort in the
> > successive patches
> >
> > Signed-off-by: Pingfan Liu <piliu@xxxxxxxxxx>
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> > Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > Cc: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>
> > Cc: Wen Xiong <wenxiong@xxxxxxxxxxxxx>
> > Cc: Baoquan He <bhe@xxxxxxxxxx>
> > Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> > Cc: kexec@xxxxxxxxxxxxxxxxxxx
> > To: linuxppc-dev@xxxxxxxxxxxxxxxx
> > ---
> > arch/powerpc/kernel/setup-common.c | 25 ++++++++++++++++++++++---
> > 1 file changed, 22 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> > index 81291e13dec0..f9ef0a2666b0 100644
> > --- a/arch/powerpc/kernel/setup-common.c
> > +++ b/arch/powerpc/kernel/setup-common.c
> > @@ -454,8 +454,8 @@ struct interrupt_server_node {
> > void __init smp_setup_cpu_maps(void)
> > {
> > struct device_node *dn;
> > - int shift = 0, cpu = 0;
> > - int j, nthreads = 1;
> > + int terminate, shift = 0, cpu = 0;
> > + int j, bt_thread = 0, nthreads = 1;
> > int len;
> > struct interrupt_server_node *intserv_node, *n;
> > struct list_head *bt_node, head;
> > @@ -518,6 +518,7 @@ void __init smp_setup_cpu_maps(void)
> > for (j = 0 ; j < nthreads; j++) {
> > if (be32_to_cpu(intserv[j]) == boot_cpu_hwid) {
> > bt_node = &intserv_node->node;
> > + bt_thread = j;
> > found_boot_cpu = true;
> > /*
> > * Record the round-shift between dt
> > @@ -537,11 +538,21 @@ void __init smp_setup_cpu_maps(void)
> > /* Select the primary thread, the boot cpu's slibing, as the logic 0 */
> > list_add_tail(&head, bt_node);
> > pr_info("the round shift between dt seq and the cpu logic number: %d\n", shift);
> > + terminate = nr_cpu_ids;
> > list_for_each_entry(intserv_node, &head, node) {
> > + j = 0;
>
> > + /* Choose a start point to cover the boot cpu */
> > + if (nr_cpu_ids - 1 < bt_thread) {
> > + /*
> > + * The processor core puts assumption on the thread id,
> > + * not to breach the assumption.
> > + */
> > + terminate = nr_cpu_ids - 1;
>
> nthreads is anyway assumed to be same for all cores. So, enforcing
> nr_cpu_ids to a minimum of nthreads (and multiple of nthreads) should
> make the code much simpler without the need for above check and the
> other complexities addressed in the subsequent patches...
>
Indeed, this series can be splited into two partsk, [1-2/5] and [3-5/5].
In [1-2/5], if smaller, the nr_cpu_ids is enforced to be equal to
nthreads. I will make it align upward on nthreads in the next version.
So [1-2/5] can be totally independent from the rest patches in this
series.
>From an engineer's perspective, [3-5/5] are added to maintain the
nr_cpus semantics. (Finally, nr_cpus=1 can be achieved but requiring
effort on other subsystem)
Testing result on my Power9 machine with SMT=4
-1. taskset -c 4 bash -c 'echo c > /proc/sysrq-trigger'
kdump:/# cat /proc/meminfo | grep Percpu
Percpu: 896 kB
kdump:/# cat /sys/devices/system/cpu/possible
0
-2. taskset -c 5 bash -c 'echo c > /proc/sysrq-trigger'
kdump:/# cat /proc/meminfo | grep Percpu
Percpu: 1792 kB
kdump:/# cat /sys/devices/system/cpu/possible
0-1
-3. taskset -c 6 bash -c 'echo c > /proc/sysrq-trigger'
kdump:/# cat /proc/meminfo | grep Percpu
Percpu: 1792 kB
kdump:/# cat /sys/devices/system/cpu/possible
0,2
-4. taskset -c 7 bash -c 'echo c > /proc/sysrq-trigger'
kdump:/# cat /proc/meminfo | grep Percpu
Percpu: 1792 kB
kdump:/# cat /sys/devices/system/cpu/possible
0,3
Thanks,
Pingfan
_______________________________________________
kexec mailing list
kexec@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/kexec
