[PATCHv9 2/2] powerpc/setup: Loosen the mapping between cpu logical id and its seq in dt
Hari Bathini
hbathini at linux.ibm.com
Tue Jan 9 15:27:08 AEDT 2024
Hi Michael,
I am fine with either approach. I was trying to address your concerns
in my way. Looking for your inputs here on how to go about this now..
On 29/11/23 7:00 am, Pingfan Liu wrote:
> Hi Hari,
>
>
> On Mon, Nov 27, 2023 at 12:30 PM Hari Bathini <hbathini at linux.ibm.com> wrote:
>>
>> Hi Pingfan, Michael,
>>
>> On 17/10/23 4:03 pm, Hari Bathini 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>
>>>
>>
>> On second thoughts, probably better off with no impact for
>> bootcpu < nr_cpu_ids case and changing only two cores logical
>> numbering otherwise. Something like the below (Please share
>> your thoughts):
>>
>
> I am afraid that it may not be as ideal as it looks, considering the
> following factors:
> -1. For the case of 'bootcpu < nr_cpu_ids', crash can happen evenly
> across any cpu in the system, which seriously undermines the
> protection intended here (Under the most optimistic scenario, there is
> a 50% chance of success)
>
> -2. For the re-ordering of logical numbering, IMHO, if there is
> concern that re-ordering will break something, the partial re-ordering
> can not avoid that. We ought to spot probable hazards so as to ease
> worries.
>
>
> Thanks,
>
> Pingfan
>
>> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
>> index ec82f5bda908..78a8312aa8c4 100644
>> --- a/arch/powerpc/kernel/prom.c
>> +++ b/arch/powerpc/kernel/prom.c
>> @@ -76,7 +76,9 @@ u64 ppc64_rma_size;
>> unsigned int boot_cpu_node_count __ro_after_init;
>> #endif
>> static phys_addr_t first_memblock_size;
>> +#ifdef CONFIG_SMP
>> static int __initdata boot_cpu_count;
>> +#endif
>>
>> static int __init early_parse_mem(char *p)
>> {
>> @@ -357,6 +359,25 @@ static int __init early_init_dt_scan_cpus(unsigned
>> long node,
>> fdt_boot_cpuid_phys(initial_boot_params)) {
>> found = boot_cpu_count;
>> found_thread = i;
>> + /*
>> + * Map boot-cpu logical id into the range
>> + * of [0, thread_per_core) if it can't be
>> + * accommodated within nr_cpu_ids.
>> + */
>> + if (i != boot_cpu_count && boot_cpu_count >= nr_cpu_ids) {
>> + boot_cpuid = i;
>> + DBG("Logical CPU number for boot CPU changed from %d to %d\n",
>> + boot_cpu_count, i);
>> + } else {
>> + boot_cpuid = boot_cpu_count;
>> + }
>> +
>> + /* Ensure boot thread is acconted for in nr_cpu_ids */
>> + if (boot_cpuid >= nr_cpu_ids) {
>> + set_nr_cpu_ids(boot_cpuid + 1);
>> + DBG("Adjusted nr_cpu_ids to %u, to include boot CPU.\n",
>> + nr_cpu_ids);
>> + }
>> }
>> #ifdef CONFIG_SMP
>> /* logical cpu id is always 0 on UP kernels */
>> @@ -368,9 +389,8 @@ static int __init early_init_dt_scan_cpus(unsigned
>> long node,
>> if (found < 0)
>> return 0;
>>
>> - DBG("boot cpu: logical %d physical %d\n", found,
>> + DBG("boot cpu: logical %d physical %d\n", boot_cpuid,
>> be32_to_cpu(intserv[found_thread]));
>> - boot_cpuid = found;
>>
>> boot_cpu_hwid = be32_to_cpu(intserv[found_thread]);
>>
>> diff --git a/arch/powerpc/kernel/setup-common.c
>> b/arch/powerpc/kernel/setup-common.c
>> index b7b733474b60..f7179525c774 100644
>> --- a/arch/powerpc/kernel/setup-common.c
>> +++ b/arch/powerpc/kernel/setup-common.c
>> @@ -409,6 +409,12 @@ static void __init cpu_init_thread_core_maps(int tpc)
>>
>> u32 *cpu_to_phys_id = NULL;
>>
>> +struct interrupt_server_node {
>> + bool avail;
>> + int len;
>> + __be32 intserv[];
>> +};
>> +
>> /**
>> * setup_cpu_maps - initialize the following cpu maps:
>> * cpu_possible_mask
>> @@ -429,9 +435,13 @@ u32 *cpu_to_phys_id = NULL;
>> */
>> void __init smp_setup_cpu_maps(void)
>> {
>> + struct interrupt_server_node *core0_node = NULL, *bt_node = NULL;
>> + int orig_boot_cpu = -1, orig_boot_thread = -1;
>> + bool found_boot_cpu = false;
>> struct device_node *dn;
>> - int cpu = 0;
>> int nthreads = 1;
>> + int cpu = 0;
>> + int j, len;
>>
>> DBG("smp_setup_cpu_maps()\n");
>>
>> @@ -442,9 +452,9 @@ void __init smp_setup_cpu_maps(void)
>> __func__, nr_cpu_ids * sizeof(u32), __alignof__(u32));
>>
>> for_each_node_by_type(dn, "cpu") {
>> + bool avail, skip = false;
>> const __be32 *intserv;
>> __be32 cpu_be;
>> - int j, len;
>>
>> DBG(" * %pOF...\n", dn);
>>
>> @@ -466,29 +476,121 @@ void __init smp_setup_cpu_maps(void)
>>
>> nthreads = len / sizeof(int);
>>
>> - for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
>> - bool avail;
>> + avail = of_device_is_available(dn);
>> + if (!avail)
>> + avail = !of_property_match_string(dn,
>> + "enable-method", "spin-table");
>> +
>> + for (j = 0; (cpu == 0 || !found_boot_cpu) && j < nthreads; j++) {
>> + if (be32_to_cpu(intserv[j]) == boot_cpu_hwid) {
>> + found_boot_cpu = true;
>> + if (cpu == 0)
>> + break;
>> +
>> + /* Original logical CPU number of thread0 in boot core */
>> + orig_boot_cpu = cpu;
>> + orig_boot_thread = j;
>> + bt_node = memblock_alloc(sizeof(struct interrupt_server_node) + len,
>> + __alignof__(u32));
>> + if (!bt_node)
>> + panic("%s: Failed to allocate %zu bytes align=0x%zx\n",
>> + __func__,
>> + sizeof(struct interrupt_server_node) + len,
>> + __alignof__(u32));
>> + bt_node->len = len;
>> + memcpy(bt_node->intserv, intserv, len);
>> + bt_node->avail = avail;
>> + skip = true;
>> + break;
>> + }
>> + }
>>
>> + /*
>> + * Boot CPU not on core0.
>> + * Hold off adding core0 until boot core is found as core0
>> + * may have to be replaced with boot core if boot core can
>> + * not be accommodated within nr_cpu_ids with its original
>> + * logical CPU numbering.
>> + */
>> + if (cpu == 0 && !found_boot_cpu) {
>> + core0_node = memblock_alloc(sizeof(struct interrupt_server_node) + len,
>> + __alignof__(u32));
>> + if (!core0_node)
>> + panic("%s: Failed to allocate %zu bytes align=0x%zx\n",
>> + __func__,
>> + sizeof(struct interrupt_server_node) + len,
>> + __alignof__(u32));
>> + core0_node->len = len;
>> + memcpy(core0_node->intserv, intserv, len);
>> + core0_node->avail = avail;
>> + skip = true;
>> + }
>> +
>> + if (skip) {
>> + /* Assumes same number of threads for all cores */
>> + cpu += nthreads;
>> + continue;
>> + }
>> +
>> + for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
>> DBG(" thread %d -> cpu %d (hard id %d)\n",
>> j, cpu, be32_to_cpu(intserv[j]));
>>
>> - avail = of_device_is_available(dn);
>> - if (!avail)
>> - avail = !of_property_match_string(dn,
>> - "enable-method", "spin-table");
>> -
>> set_cpu_present(cpu, avail);
>> set_cpu_possible(cpu, true);
>> cpu_to_phys_id[cpu] = be32_to_cpu(intserv[j]);
>> cpu++;
>> }
>>
>> - if (cpu >= nr_cpu_ids) {
>> + if (found_boot_cpu && cpu >= nr_cpu_ids) {
>> of_node_put(dn);
>> break;
>> }
>> }
>>
>> + /*
>> + * Boot CPU not on core0.
>> + *
>> + * If nr_cpu_ids does not accommodate the original logical CPU
>> numbering for
>> + * boot CPU core, use logical CPU numbers 0 to nthreads for boot CPU core.
>> + * Note that boot cpu is already assigned with logical CPU number
>> somewhere
>> + * between 0 to nthreads (depending on the boot thread within the core) in
>> + * early_init_dt_scan_cpus() for this case.
>> + *
>> + * Otherwise, stick with the original logical CPU numbering.
>> + */
>> + if (bt_node) {
>> + int core0_cpu;
>> +
>> + if (orig_boot_cpu + orig_boot_thread >= nr_cpu_ids) {
>> + cpu = 0;
>> + core0_cpu = orig_boot_cpu;
>> + } else {
>> + cpu = orig_boot_cpu;
>> + core0_cpu = 0;
>> + }
>> +
>> + for (j = 0; j < nthreads && core0_cpu < nr_cpu_ids; j++) {
>> + DBG(" thread %d -> cpu %d (hard id %d)\n",
>> + j, core0_cpu, be32_to_cpu(core0_node->intserv[j]));
>> +
>> + set_cpu_present(core0_cpu, core0_node->avail);
>> + set_cpu_possible(core0_cpu, true);
>> + cpu_to_phys_id[core0_cpu] = be32_to_cpu(core0_node->intserv[j]);
>> + core0_cpu++;
>> + }
>> +
>> + for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
>> + DBG(" thread %d -> cpu %d (hard id %d)\n",
>> + j, cpu, be32_to_cpu(bt_node->intserv[j]));
>> +
>> + set_cpu_present(cpu, bt_node->avail);
>> + set_cpu_possible(cpu, true);
>> + cpu_to_phys_id[cpu] = be32_to_cpu(bt_node->intserv[j]);
>> + cpu++;
>> + }
>> + }
>> +
>> /* If no SMT supported, nthreads is forced to 1 */
>> if (!cpu_has_feature(CPU_FTR_SMT)) {
>> DBG(" SMT disabled ! nthreads forced to 1\n");
>>
>
Thanks
Hari
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