[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 15:33:02 AEDT 2024
On 09/01/24 9:57 am, Hari Bathini wrote:
> Hi Michael,
>
Sorry, Michael.
I am just about getting back to work and I spoke too soon.
You already seem to have posted a set with the approach you had in mind:
https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=388350
Thanks
Hari
> 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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