On Mon, 2018-03-12 at 12:43 +0800, Pingfan Liu wrote:
> For kexec -p, the boot cpu can be not the cpu0, this causes the problem
> to alloc paca[]. In theory, there is no requirement to assign cpu's logical
> id as its present seq by device tree. But we have something like
> cpu_first_thread_sibling(), which makes assumption on the mapping inside
> a core. Hence partially changing the mapping, i.e. unbind the mapping of
> core while keep the mapping inside a core. After this patch, boot-cpu
> will always be mapped into the range [0,threads_per_core).
I'm ok with the idea but not fan of the implementation:
> Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> ---
> arch/powerpc/include/asm/smp.h | 1 +
> arch/powerpc/kernel/prom.c | 25 ++++++++++++++-----------
> arch/powerpc/kernel/setup-common.c | 21 +++++++++++++++++++++
> 3 files changed, 36 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
> index fac963e..1299100 100644
> --- a/arch/powerpc/include/asm/smp.h
> +++ b/arch/powerpc/include/asm/smp.h
> @@ -30,6 +30,7 @@
> #include <asm/percpu.h>
>
> extern int boot_cpuid;
> +extern int boot_cpuhwid;
> extern int spinning_secondaries;
>
> extern void cpu_die(void);
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index da67606..d0ebb25 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -315,8 +315,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
> const __be32 *intserv;
> int i, nthreads;
> int len;
> - int found = -1;
> - int found_thread = 0;
> + bool found = false;
>
> /* We are scanning "cpu" nodes only */
> if (type == NULL || strcmp(type, "cpu") != 0)
> @@ -341,8 +340,11 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
> if (fdt_version(initial_boot_params) >= 2) {
> if (be32_to_cpu(intserv[i]) ==
> fdt_boot_cpuid_phys(initial_boot_params)) {
> - found = boot_cpu_count;
> - found_thread = i;
> + /* always map the boot-cpu logical id into the
> + * the range of [0, thread_per_core)
> + */
> + boot_cpuid = i;
> + found = true;
> }
Call it boot_thread_id
> } else {
> /*
> @@ -351,8 +353,10 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
> * off secondary threads.
> */
> if (of_get_flat_dt_prop(node,
> - "linux,boot-cpu", NULL) != NULL)
> - found = boot_cpu_count;
> + "linux,boot-cpu", NULL) != NULL) {
> + boot_cpuid = i;
> + found = true;
> + }
> }
> #ifdef CONFIG_SMP
> /* logical cpu id is always 0 on UP kernels */
> @@ -361,13 +365,12 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
> }
>
> /* Not the boot CPU */
> - if (found < 0)
> + if (!found)
> return 0;
>
> - DBG("boot cpu: logical %d physical %d\n", found,
> - be32_to_cpu(intserv[found_thread]));
> - boot_cpuid = found;
> - set_hard_smp_processor_id(found, be32_to_cpu(intserv[found_thread]));
> + boot_cpuhwid = be32_to_cpu(intserv[boot_cpuid]);
> + DBG("boot cpu: logical %d physical %d\n", boot_cpuid, boot_cpuhwid);
> + set_hard_smp_processor_id(boot_cpuid, boot_cpuhwid);
>
> /*
> * PAPR defines "logical" PVR values for cpus that
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index 66f7cc6..1a67344 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -86,6 +86,7 @@ struct machdep_calls *machine_id;
> EXPORT_SYMBOL(machine_id);
>
> int boot_cpuid = -1;
> +int boot_cpuhwid = -1;
> EXPORT_SYMBOL_GPL(boot_cpuid);
>
> /*
> @@ -459,11 +460,17 @@ static void __init cpu_init_thread_core_maps(int tpc)
> void __init smp_setup_cpu_maps(void)
> {
> struct device_node *dn;
> + struct device_node *boot_dn = NULL;
> + bool handling_bootdn = true;
> int cpu = 0;
> int nthreads = 1;
>
> DBG("smp_setup_cpu_maps()\n");
>
> +again:
> + /* E.g. kexec will not boot from the 1st core. So firstly loop to find out
> + * the dn of boot-cpu, and map them onto [0, nthreads)
> + */
> for_each_node_by_type(dn, "cpu") {
> const __be32 *intserv;
> __be32 cpu_be;
> @@ -488,6 +495,16 @@ void __init smp_setup_cpu_maps(void)
>
> nthreads = len / sizeof(int);
>
> + if (handling_bootdn) {
> + if (boot_cpuid < nthreads &&
> + be32_to_cpu(intserv[boot_cpuid]) == boot_cpuhwid) {
> + boot_dn = dn;
> + }
> + if (boot_dn == NULL)
> + continue;
> + } else if (dn == boot_dn)
> + continue;
> +
> for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
> bool avail;
>
> @@ -509,6 +526,10 @@ void __init smp_setup_cpu_maps(void)
> of_node_put(dn);
> break;
> }
> + if (handling_bootdn) {
> + handling_bootdn = false;
> + goto again;
> + }
> }
You don't need that "again" loop and "handling_bootdn" weird boolean.
Instead, start with cpu = 1 instead of cpu = 0, and rename it to
"next_cpu".
Then, before the thread loop, check if we are on the same core
as boot_cpuhwid:
if (same_core_as_boot_cpu(intserv)) {
cpu = 0;
} else if (next_cpu < nr_cpus_ids) {
cpu = next_cpu++;
} else {
of_node_put(dn);
break;
}
>
> /* If no SMT supported, nthreads is forced to 1 */
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