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Message-ID: <20240925-2acd8d9743cf40b999172b40@orel>
Date: Wed, 25 Sep 2024 15:54:28 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Xu Lu <luxu.kernel@...edance.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
andy.chiu@...ive.com, guoren@...nel.org, christoph.muellner@...ll.eu,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, lihangjing@...edance.com,
dengliang.1214@...edance.com, xieyongji@...edance.com, chaiwen.cc@...edance.com
Subject: Re: [PATCH v3 1/2] riscv: process: Introduce idle thread using Zawrs
extension
On Wed, Sep 25, 2024 at 09:15:46PM GMT, Xu Lu wrote:
> The Zawrs extension introduces a new instruction WRS.NTO, which will
> register a reservation set and causes the hart to temporarily stall
> execution in a low-power state until a store occurs to the reservation
> set or an interrupt is observed.
>
> This commit implements new version of idle thread for RISC-V via Zawrs
> extension.
>
> Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
> Reviewed-by: Hangjing Li <lihangjing@...edance.com>
> Reviewed-by: Liang Deng <dengliang.1214@...edance.com>
> Reviewed-by: Wen Chai <chaiwen.cc@...edance.com>
> ---
> arch/riscv/Kconfig | 10 ++++++++
> arch/riscv/include/asm/cpuidle.h | 11 +-------
> arch/riscv/include/asm/processor.h | 18 +++++++++++++
> arch/riscv/kernel/cpu.c | 5 ++++
> arch/riscv/kernel/process.c | 41 +++++++++++++++++++++++++++++-
> 5 files changed, 74 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 939ea7f6a228..56cf6000d286 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -23,6 +23,7 @@ config RISCV
> select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
> select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
> select ARCH_HAS_BINFMT_FLAT
> + select ARCH_HAS_CPU_FINALIZE_INIT
> select ARCH_HAS_CURRENT_STACK_POINTER
> select ARCH_HAS_DEBUG_VIRTUAL if MMU
> select ARCH_HAS_DEBUG_VM_PGTABLE
> @@ -1153,6 +1154,15 @@ endmenu # "Power management options"
>
> menu "CPU Power Management"
>
> +config RISCV_ZAWRS_IDLE
> + bool "Idle thread using ZAWRS extensions"
> + depends on RISCV_ISA_ZAWRS
> + default y
> + help
> + Adds support to implement idle thread using ZAWRS extension.
> +
> + If you don't know what to do here, say Y.
> +
> source "drivers/cpuidle/Kconfig"
>
> source "drivers/cpufreq/Kconfig"
> diff --git a/arch/riscv/include/asm/cpuidle.h b/arch/riscv/include/asm/cpuidle.h
> index 71fdc607d4bc..94c9ecb46571 100644
> --- a/arch/riscv/include/asm/cpuidle.h
> +++ b/arch/riscv/include/asm/cpuidle.h
> @@ -10,15 +10,6 @@
> #include <asm/barrier.h>
> #include <asm/processor.h>
>
> -static inline void cpu_do_idle(void)
> -{
> - /*
> - * Add mb() here to ensure that all
> - * IO/MEM accesses are completed prior
> - * to entering WFI.
> - */
> - mb();
> - wait_for_interrupt();
> -}
> +void cpu_do_idle(void);
>
> #endif
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index efa1b3519b23..d0dcdb7e7392 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -12,6 +12,7 @@
>
> #include <vdso/processor.h>
>
> +#include <asm/insn-def.h>
> #include <asm/ptrace.h>
>
> #define arch_get_mmap_end(addr, len, flags) \
> @@ -148,6 +149,21 @@ static inline void wait_for_interrupt(void)
> __asm__ __volatile__ ("wfi");
> }
>
> +static inline void wrs_nto(unsigned long *addr)
> +{
> + int val;
> +
> + __asm__ __volatile__(
> +#ifdef CONFIG_64BIT
> + "lr.d %[p], %[v]\n\t"
> +#else
> + "lr.w %[p], %[v]\n\t"
> +#endif
val is always 32-bit since it's an int. We should always use lr.w.
> + ZAWRS_WRS_NTO "\n\t"
> + : [p] "=&r" (val), [v] "+A" (*addr)
What do 'p' and 'v' represent? If they are pointer and value then they're
backwards. I would just spell them out [val] and [addr].
> + : : "memory");
> +}
> +
> extern phys_addr_t dma32_phys_limit;
>
> struct device_node;
> @@ -177,6 +193,8 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
> #define RISCV_SET_ICACHE_FLUSH_CTX(arg1, arg2) riscv_set_icache_flush_ctx(arg1, arg2)
> extern int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread);
>
> +extern void select_idle_routine(void);
> +
> #endif /* __ASSEMBLY__ */
>
> #endif /* _ASM_RISCV_PROCESSOR_H */
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index f6b13e9f5e6c..97a7144fa6cd 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -23,6 +23,11 @@ bool arch_match_cpu_phys_id(int cpu, u64 phys_id)
> return phys_id == cpuid_to_hartid_map(cpu);
> }
>
> +void __init arch_cpu_finalize_init(void)
> +{
> + select_idle_routine();
> +}
Is there a reason we need to do this at arch_cpu_finalize_init() time?
This seems like the type of thing we have typically done at the bottom of
setup_arch().
> +
> /*
> * Returns the hart ID of the given device tree node, or -ENODEV if the node
> * isn't an enabled and valid RISC-V hart node.
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index e4bc61c4e58a..77769965609e 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -15,6 +15,7 @@
> #include <linux/tick.h>
> #include <linux/ptrace.h>
> #include <linux/uaccess.h>
> +#include <linux/static_call.h>
>
> #include <asm/unistd.h>
> #include <asm/processor.h>
> @@ -35,11 +36,49 @@ EXPORT_SYMBOL(__stack_chk_guard);
>
> extern asmlinkage void ret_from_fork(void);
>
> -void noinstr arch_cpu_idle(void)
> +static __cpuidle void default_idle(void)
> +{
> + /*
> + * Add mb() here to ensure that all
> + * IO/MEM accesses are completed prior
> + * to entering WFI.
> + */
> + mb();
> + wait_for_interrupt();
> +}
> +
> +static __cpuidle void wrs_idle(void)
> +{
> + /*
> + * Add mb() here to ensure that all
> + * IO/MEM accesses are completed prior
> + * to entering WRS.NTO.
> + */
> + mb();
> + wrs_nto(¤t_thread_info()->flags);
> +}
> +
> +DEFINE_STATIC_CALL_NULL(riscv_idle, default_idle);
> +
> +void __cpuidle cpu_do_idle(void)
> +{
> + static_call(riscv_idle)();
> +}
> +
> +void __cpuidle arch_cpu_idle(void)
Switching the section of this from '.noinstr.text' to 'cpuidle.text'
should probably be a separate patch.
> {
> cpu_do_idle();
> }
>
> +void __init select_idle_routine(void)
> +{
> + if (IS_ENABLED(CONFIG_RISCV_ZAWRS_IDLE) &&
> + riscv_has_extension_likely(RISCV_ISA_EXT_ZAWRS))
> + static_call_update(riscv_idle, wrs_idle);
> + else
> + static_call_update(riscv_idle, default_idle);
Do we need this 'else'? Can't we set the default at DEFINE_STATIC_CALL*
time?
> +}
> +
> int set_unalign_ctl(struct task_struct *tsk, unsigned int val)
> {
> if (!unaligned_ctl_available())
> --
> 2.20.1
>
Thanks,
drew
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