Messages in this thread | | | From | Anup Patel <> | Date | Thu, 16 Aug 2018 11:09:48 +0530 | Subject | Re: [RFC PATCH 1/5] RISC-V: Add logical CPU indexing for RISC-V |
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On Thu, Aug 16, 2018 at 10:47 AM, Atish Patra <atish.patra@wdc.com> wrote: > On 8/15/18 9:06 PM, Anup Patel wrote: >> >> On Thu, Aug 16, 2018 at 5:26 AM, Atish Patra <atish.patra@wdc.com> wrote: >>> >>> Currently, both linux cpu id and hardware cpu id are same. >>> This is not recommended as it will lead to discontinuous cpu >>> indexing in Linux. Moreover, kdump kernel will run from CPU0 >>> which would be absent if we follow existing scheme. >>> >>> Implement a logical mapping between Linux cpu id and hardware >>> cpuid to decouple these two. Always mark the boot processor as >>> cpu0 and all other cpus get the logical cpu id based on their >>> booting order. >>> >>> Signed-off-by: Atish Patra <atish.patra@wdc.com> >>> --- >>> arch/riscv/include/asm/smp.h | 17 ++++++++++++++++- >>> arch/riscv/kernel/setup.c | 2 ++ >>> arch/riscv/kernel/smp.c | 19 +++++++++++++++++++ >>> 3 files changed, 37 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h >>> index 36016845..0763337b 100644 >>> --- a/arch/riscv/include/asm/smp.h >>> +++ b/arch/riscv/include/asm/smp.h >>> @@ -22,6 +22,12 @@ >>> #include <linux/cpumask.h> >>> #include <linux/irqreturn.h> >>> >>> +/* >>> + * Mapping between linux logical cpu index and hartid. >>> + */ >>> +extern u64 __cpu_logical_map[NR_CPUS]; >>> +#define cpu_logical_map(cpu) __cpu_logical_map[cpu] >>> + >>> #ifdef CONFIG_SMP >>> >>> /* SMP initialization hook for setup_arch */ >>> @@ -33,6 +39,8 @@ void arch_send_call_function_ipi_mask(struct cpumask >>> *mask); >>> /* Hook for the generic smp_call_function_single() routine. */ >>> void arch_send_call_function_single_ipi(int cpu); >>> >>> +int riscv_hartid_to_cpuid(int hartid); >>> +void cpuid_to_hartid_mask(const struct cpumask *in, struct cpumask >>> *out); >>> /* >>> * This is particularly ugly: it appears we can't actually get the >>> definition >>> * of task_struct here, but we need access to the CPU this task is >>> running on. >>> @@ -41,6 +49,13 @@ void arch_send_call_function_single_ipi(int cpu); >>> */ >>> #define raw_smp_processor_id() (*((int*)((char*)get_current() + >>> TASK_TI_CPU))) >>> >>> -#endif /* CONFIG_SMP */ >>> +#else >>> + >>> +static inline int riscv_hartid_to_cpuid(int hartid) { return 0 ; } >>> +static inline void cpuid_to_hartid_mask(const struct cpumask *in, >>> + struct cpumask *out) { >>> + cpumask_set_cpu(cpu_logical_map(0), out); >>> +} >>> >>> +#endif /* CONFIG_SMP */ >>> #endif /* _ASM_RISCV_SMP_H */ >>> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c >>> index db20dc63..e21ed481 100644 >>> --- a/arch/riscv/kernel/setup.c >>> +++ b/arch/riscv/kernel/setup.c >>> @@ -82,6 +82,8 @@ EXPORT_SYMBOL(empty_zero_page); >>> /* The lucky hart to first increment this variable will boot the other >>> cores */ >>> atomic_t hart_lottery; >>> >>> +u64 __cpu_logical_map[NR_CPUS]; >> >> >> If hardware IDs are always machine word size then its better to use >> "unsigned long" in-place of u64. >> > > Good point. Thanks. > >> The __cpu_logical_map[] should be zero initially because zero is a >> valid hardware ID. Better set all entries to -1 by assigning { -1 } to the >> array. >> > > ok. I will introduce INVALID_HART_ID (=-1) and initialize with that. > >> Also, I feel __cpu_logical_map[] should be part of smp.c instead of >> setup.c. Any particular reason for having it in setup.c? >> > > currently smp.c is only compiled in if CONFIG_SMP. That's why I kept it in > setup.c
Ahh, got it. For now let it be here till we figure better place for it.
Regards, Anup
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