Messages in this thread Patch in this message | | | From | Charlie Jenkins <> | Date | Tue, 27 Feb 2024 15:13:14 -0800 | Subject | [PATCH v5 2/2] riscv: Set unaligned access speed at compile time |
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Introduce Kconfig options to set the kernel unaligned access support. These options provide a non-portable alternative to the runtime unaligned access probe.
To support this, the unaligned access probing code is moved into it's own file and gated behind a new RISCV_PROBE_UNALIGNED_ACCESS_SUPPORT option.
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com> --- arch/riscv/Kconfig | 47 +++++- arch/riscv/include/asm/cpufeature.h | 32 +++- arch/riscv/kernel/Makefile | 6 +- arch/riscv/kernel/cpufeature.c | 255 ------------------------------ arch/riscv/kernel/probe_emulated_access.c | 64 ++++++++ arch/riscv/kernel/sys_hwprobe.c | 23 +++ arch/riscv/kernel/traps_misaligned.c | 54 +------ 7 files changed, 163 insertions(+), 318 deletions(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index bffbd869a068..ad0a9c1f8802 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -690,25 +690,58 @@ config THREAD_SIZE_ORDER config RISCV_MISALIGNED bool "Support misaligned load/store traps for kernel and userspace" select SYSCTL_ARCH_UNALIGN_ALLOW + depends on RISCV_PROBE_UNALIGNED_ACCESS || RISCV_EMULATED_UNALIGNED_ACCESS default y help Say Y here if you want the kernel to embed support for misaligned load/store for both kernel and userspace. When disable, misaligned accesses will generate SIGBUS in userspace and panic in kernel. +choice + prompt "Unaligned Accesses Support" + default RISCV_PROBE_UNALIGNED_ACCESS + help + This selects the hardware support for unaligned accesses. This + information is used by the kernel to perform optimizations. It is also + exposed to user space via the hwprobe syscall. The hardware will be + probed at boot by default. + +config RISCV_PROBE_UNALIGNED_ACCESS + bool "Probe for hardware unaligned access support" + help + During boot, the kernel will run a series of tests to determine the + speed of unaligned accesses. This probing will dynamically determine + the speed of unaligned accesses on the boot hardware. + +config RISCV_EMULATED_UNALIGNED_ACCESS + bool "Assume the system expects emulated unaligned memory accesses" + help + Assume that the system expects emulated unaligned memory accesses. + When enabled, this option notifies the kernel and userspace that + unaligned memory accesses will be emulated by either the kernel or + firmware. + +config RISCV_SLOW_UNALIGNED_ACCESS + bool "Assume the system supports slow unaligned memory accesses" + depends on NONPORTABLE + help + Assume that the system supports slow unaligned memory accesses. The + kernel may not be able to run at all on systems that do not support + unaligned memory accesses. + config RISCV_EFFICIENT_UNALIGNED_ACCESS - bool "Assume the CPU supports fast unaligned memory accesses" + bool "Assume the system supports fast unaligned memory accesses" depends on NONPORTABLE select DCACHE_WORD_ACCESS if MMU select HAVE_EFFICIENT_UNALIGNED_ACCESS help - Say Y here if you want the kernel to assume that the CPU supports - efficient unaligned memory accesses. When enabled, this option - improves the performance of the kernel on such CPUs. However, the - kernel will run much more slowly, or will not be able to run at all, - on CPUs that do not support efficient unaligned memory accesses. + Assume that the system supports fast unaligned memory accesses. When + enabled, this option improves the performance of the kernel on such + systems. However, the kernel will run much more slowly, or will not + be able to run at all, on systems that do not support efficient + unaligned memory accesses. - If unsure what to do here, say N. +endchoice endmenu # "Platform type" diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h index 466e1f591919..cd166b0e52c4 100644 --- a/arch/riscv/include/asm/cpufeature.h +++ b/arch/riscv/include/asm/cpufeature.h @@ -28,17 +28,29 @@ struct riscv_isainfo { DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo); -DECLARE_PER_CPU(long, misaligned_access_speed); - /* Per-cpu ISA extensions. */ extern struct riscv_isainfo hart_isa[NR_CPUS]; void riscv_user_isa_enable(void); -#ifdef CONFIG_RISCV_MISALIGNED +#if defined(CONFIG_RISCV_MISALIGNED) +#if defined(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS) bool unaligned_ctl_available(void); bool check_unaligned_access_emulated(int cpu); void unaligned_emulation_finish(void); +#elif defined(CONFIG_RISCV_EMULATED_UNALIGNED_ACCESS) +static inline bool unaligned_ctl_available(void) +{ + return true; +} + +static inline bool check_unaligned_access_emulated(int cpu) +{ + return true; +} + +static inline void unaligned_emulation_finish(void) {} +#endif #else static inline bool unaligned_ctl_available(void) { @@ -53,12 +65,26 @@ static inline bool check_unaligned_access_emulated(int cpu) static inline void unaligned_emulation_finish(void) {} #endif +#if defined(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS) +DECLARE_PER_CPU(long, misaligned_access_speed); + DECLARE_STATIC_KEY_FALSE(fast_unaligned_access_speed_key); static __always_inline bool has_fast_unaligned_accesses(void) { return static_branch_likely(&fast_unaligned_access_speed_key); } +#elif defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) +static __always_inline bool has_fast_unaligned_accesses(void) +{ + return true; +} +#else +static __always_inline bool has_fast_unaligned_accesses(void) +{ + return false; +} +#endif unsigned long riscv_get_elf_hwcap(void); diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile index f71910718053..3355ef87684a 100644 --- a/arch/riscv/kernel/Makefile +++ b/arch/riscv/kernel/Makefile @@ -38,7 +38,6 @@ extra-y += vmlinux.lds obj-y += head.o obj-y += soc.o obj-$(CONFIG_RISCV_ALTERNATIVE) += alternative.o -obj-y += copy-unaligned.o obj-y += cpu.o obj-y += cpufeature.o obj-y += entry.o @@ -62,6 +61,11 @@ obj-y += tests/ obj-$(CONFIG_MMU) += vdso.o vdso/ obj-$(CONFIG_RISCV_MISALIGNED) += traps_misaligned.o +ifeq ($(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS), y) +obj-y += copy-unaligned.o +obj-y += unaligned_access_speed.o +obj-$(CONFIG_RISCV_MISALIGNED) += probe_emulated_access.o +endif obj-$(CONFIG_FPU) += fpu.o obj-$(CONFIG_RISCV_ISA_V) += vector.o obj-$(CONFIG_RISCV_ISA_V) += kernel_mode_vector.o diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 7878cddccc0d..319670af5704 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -11,7 +11,6 @@ #include <linux/cpu.h> #include <linux/cpuhotplug.h> #include <linux/ctype.h> -#include <linux/jump_label.h> #include <linux/log2.h> #include <linux/memory.h> #include <linux/module.h> @@ -21,20 +20,12 @@ #include <asm/cacheflush.h> #include <asm/cpufeature.h> #include <asm/hwcap.h> -#include <asm/hwprobe.h> #include <asm/patch.h> #include <asm/processor.h> #include <asm/vector.h> -#include "copy-unaligned.h" - #define NUM_ALPHA_EXTS ('z' - 'a' + 1) -#define MISALIGNED_ACCESS_JIFFIES_LG2 1 -#define MISALIGNED_BUFFER_SIZE 0x4000 -#define MISALIGNED_BUFFER_ORDER get_order(MISALIGNED_BUFFER_SIZE) -#define MISALIGNED_COPY_SIZE ((MISALIGNED_BUFFER_SIZE / 2) - 0x80) - unsigned long elf_hwcap __read_mostly; /* Host ISA bitmap */ @@ -43,11 +34,6 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly; /* Per-cpu ISA extensions. */ struct riscv_isainfo hart_isa[NR_CPUS]; -/* Performance information */ -DEFINE_PER_CPU(long, misaligned_access_speed); - -static cpumask_t fast_misaligned_access; - /** * riscv_isa_extension_base() - Get base extension word * @@ -706,247 +692,6 @@ unsigned long riscv_get_elf_hwcap(void) return hwcap; } -static int check_unaligned_access(void *param) -{ - int cpu = smp_processor_id(); - u64 start_cycles, end_cycles; - u64 word_cycles; - u64 byte_cycles; - int ratio; - unsigned long start_jiffies, now; - struct page *page = param; - void *dst; - void *src; - long speed = RISCV_HWPROBE_MISALIGNED_SLOW; - - if (check_unaligned_access_emulated(cpu)) - return 0; - - /* Make an unaligned destination buffer. */ - dst = (void *)((unsigned long)page_address(page) | 0x1); - /* Unalign src as well, but differently (off by 1 + 2 = 3). */ - src = dst + (MISALIGNED_BUFFER_SIZE / 2); - src += 2; - word_cycles = -1ULL; - /* Do a warmup. */ - __riscv_copy_words_unaligned(dst, src, MISALIGNED_COPY_SIZE); - preempt_disable(); - start_jiffies = jiffies; - while ((now = jiffies) == start_jiffies) - cpu_relax(); - - /* - * For a fixed amount of time, repeatedly try the function, and take - * the best time in cycles as the measurement. - */ - while (time_before(jiffies, now + (1 << MISALIGNED_ACCESS_JIFFIES_LG2))) { - start_cycles = get_cycles64(); - /* Ensure the CSR read can't reorder WRT to the copy. */ - mb(); - __riscv_copy_words_unaligned(dst, src, MISALIGNED_COPY_SIZE); - /* Ensure the copy ends before the end time is snapped. */ - mb(); - end_cycles = get_cycles64(); - if ((end_cycles - start_cycles) < word_cycles) - word_cycles = end_cycles - start_cycles; - } - - byte_cycles = -1ULL; - __riscv_copy_bytes_unaligned(dst, src, MISALIGNED_COPY_SIZE); - start_jiffies = jiffies; - while ((now = jiffies) == start_jiffies) - cpu_relax(); - - while (time_before(jiffies, now + (1 << MISALIGNED_ACCESS_JIFFIES_LG2))) { - start_cycles = get_cycles64(); - mb(); - __riscv_copy_bytes_unaligned(dst, src, MISALIGNED_COPY_SIZE); - mb(); - end_cycles = get_cycles64(); - if ((end_cycles - start_cycles) < byte_cycles) - byte_cycles = end_cycles - start_cycles; - } - - preempt_enable(); - - /* Don't divide by zero. */ - if (!word_cycles || !byte_cycles) { - pr_warn("cpu%d: rdtime lacks granularity needed to measure unaligned access speed\n", - cpu); - - return 0; - } - - if (word_cycles < byte_cycles) - speed = RISCV_HWPROBE_MISALIGNED_FAST; - - ratio = div_u64((byte_cycles * 100), word_cycles); - pr_info("cpu%d: Ratio of byte access time to unaligned word access is %d.%02d, unaligned accesses are %s\n", - cpu, - ratio / 100, - ratio % 100, - (speed == RISCV_HWPROBE_MISALIGNED_FAST) ? "fast" : "slow"); - - per_cpu(misaligned_access_speed, cpu) = speed; - - /* - * Set the value of fast_misaligned_access of a CPU. These operations - * are atomic to avoid race conditions. - */ - if (speed == RISCV_HWPROBE_MISALIGNED_FAST) - cpumask_set_cpu(cpu, &fast_misaligned_access); - else - cpumask_clear_cpu(cpu, &fast_misaligned_access); - - return 0; -} - -static void check_unaligned_access_nonboot_cpu(void *param) -{ - unsigned int cpu = smp_processor_id(); - struct page **pages = param; - - if (smp_processor_id() != 0) - check_unaligned_access(pages[cpu]); -} - -DEFINE_STATIC_KEY_FALSE(fast_unaligned_access_speed_key); - -static void modify_unaligned_access_branches(cpumask_t *mask, int weight) -{ - if (cpumask_weight(mask) == weight) - static_branch_enable_cpuslocked(&fast_unaligned_access_speed_key); - else - static_branch_disable_cpuslocked(&fast_unaligned_access_speed_key); -} - -static void set_unaligned_access_static_branches_except_cpu(int cpu) -{ - /* - * Same as set_unaligned_access_static_branches, except excludes the - * given CPU from the result. When a CPU is hotplugged into an offline - * state, this function is called before the CPU is set to offline in - * the cpumask, and thus the CPU needs to be explicitly excluded. - */ - - cpumask_t fast_except_me; - - cpumask_and(&fast_except_me, &fast_misaligned_access, cpu_online_mask); - cpumask_clear_cpu(cpu, &fast_except_me); - - modify_unaligned_access_branches(&fast_except_me, num_online_cpus() - 1); -} - -static void set_unaligned_access_static_branches(void) -{ - /* - * This will be called after check_unaligned_access_all_cpus so the - * result of unaligned access speed for all CPUs will be available. - * - * To avoid the number of online cpus changing between reading - * cpu_online_mask and calling num_online_cpus, cpus_read_lock must be - * held before calling this function. - */ - - cpumask_t fast_and_online; - - cpumask_and(&fast_and_online, &fast_misaligned_access, cpu_online_mask); - - modify_unaligned_access_branches(&fast_and_online, num_online_cpus()); -} - -static int lock_and_set_unaligned_access_static_branch(void) -{ - cpus_read_lock(); - set_unaligned_access_static_branches(); - cpus_read_unlock(); - - return 0; -} - -arch_initcall_sync(lock_and_set_unaligned_access_static_branch); - -static int riscv_online_cpu(unsigned int cpu) -{ - static struct page *buf; - - /* We are already set since the last check */ - if (per_cpu(misaligned_access_speed, cpu) != RISCV_HWPROBE_MISALIGNED_UNKNOWN) - goto exit; - - buf = alloc_pages(GFP_KERNEL, MISALIGNED_BUFFER_ORDER); - if (!buf) { - pr_warn("Allocation failure, not measuring misaligned performance\n"); - return -ENOMEM; - } - - check_unaligned_access(buf); - __free_pages(buf, MISALIGNED_BUFFER_ORDER); - -exit: - set_unaligned_access_static_branches(); - - return 0; -} - -static int riscv_offline_cpu(unsigned int cpu) -{ - set_unaligned_access_static_branches_except_cpu(cpu); - - return 0; -} - -/* Measure unaligned access on all CPUs present at boot in parallel. */ -static int check_unaligned_access_all_cpus(void) -{ - unsigned int cpu; - unsigned int cpu_count = num_possible_cpus(); - struct page **bufs = kzalloc(cpu_count * sizeof(struct page *), - GFP_KERNEL); - - if (!bufs) { - pr_warn("Allocation failure, not measuring misaligned performance\n"); - return 0; - } - - /* - * Allocate separate buffers for each CPU so there's no fighting over - * cache lines. - */ - for_each_cpu(cpu, cpu_online_mask) { - bufs[cpu] = alloc_pages(GFP_KERNEL, MISALIGNED_BUFFER_ORDER); - if (!bufs[cpu]) { - pr_warn("Allocation failure, not measuring misaligned performance\n"); - goto out; - } - } - - /* Check everybody except 0, who stays behind to tend jiffies. */ - on_each_cpu(check_unaligned_access_nonboot_cpu, bufs, 1); - - /* Check core 0. */ - smp_call_on_cpu(0, check_unaligned_access, bufs[0], true); - - /* - * Setup hotplug callbacks for any new CPUs that come online or go - * offline. - */ - cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "riscv:online", - riscv_online_cpu, riscv_offline_cpu); - -out: - unaligned_emulation_finish(); - for_each_cpu(cpu, cpu_online_mask) { - if (bufs[cpu]) - __free_pages(bufs[cpu], MISALIGNED_BUFFER_ORDER); - } - - kfree(bufs); - return 0; -} - -arch_initcall(check_unaligned_access_all_cpus); - void riscv_user_isa_enable(void) { if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ)) diff --git a/arch/riscv/kernel/probe_emulated_access.c b/arch/riscv/kernel/probe_emulated_access.c new file mode 100644 index 000000000000..5f65b31c7558 --- /dev/null +++ b/arch/riscv/kernel/probe_emulated_access.c @@ -0,0 +1,64 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright 2024 Rivos Inc. + */ + +#include <linux/cache.h> +#include <linux/cpumask.h> +#include <linux/types.h> +#include <linux/percpu-defs.h> +#include <linux/printk.h> +#include <asm/cpufeature.h> +#include <asm/hwprobe.h> + +static bool unaligned_ctl __read_mostly; + +bool check_unaligned_access_emulated(int cpu) +{ + long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu); + unsigned long tmp_var, tmp_val; + bool misaligned_emu_detected; + + *mas_ptr = RISCV_HWPROBE_MISALIGNED_UNKNOWN; + + __asm__ __volatile__ ( + " "REG_L" %[tmp], 1(%[ptr])\n" + : [tmp] "=r" (tmp_val) : [ptr] "r" (&tmp_var) : "memory"); + + misaligned_emu_detected = (*mas_ptr == RISCV_HWPROBE_MISALIGNED_EMULATED); + /* + * If unaligned_ctl is already set, this means that we detected that all + * CPUS uses emulated misaligned access at boot time. If that changed + * when hotplugging the new cpu, this is something we don't handle. + */ + if (unlikely(unaligned_ctl && !misaligned_emu_detected)) { + pr_crit("CPU misaligned accesses non homogeneous (expected all emulated)\n"); + while (true) + cpu_relax(); + } + + return misaligned_emu_detected; +} + +void unaligned_emulation_finish(void) +{ + int cpu; + + /* + * We can only support PR_UNALIGN controls if all CPUs have misaligned + * accesses emulated since tasks requesting such control can run on any + * CPU. + */ + for_each_present_cpu(cpu) { + if (per_cpu(misaligned_access_speed, cpu) != + RISCV_HWPROBE_MISALIGNED_EMULATED) { + return; + } + } + unaligned_ctl = true; +} + +bool unaligned_ctl_available(void) +{ + return unaligned_ctl; +} diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c index a7c56b41efd2..69df8eaad9e7 100644 --- a/arch/riscv/kernel/sys_hwprobe.c +++ b/arch/riscv/kernel/sys_hwprobe.c @@ -147,8 +147,10 @@ static bool hwprobe_ext0_has(const struct cpumask *cpus, unsigned long ext) return (pair.value & ext); } +#if defined(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS) static u64 hwprobe_misaligned(const struct cpumask *cpus) { + return RISCV_HWPROBE_MISALIGNED_FAST; int cpu; u64 perf = -1ULL; @@ -169,6 +171,27 @@ static u64 hwprobe_misaligned(const struct cpumask *cpus) return perf; } +#elif defined(CONFIG_RISCV_EMULATED_UNALIGNED_ACCESS) +static u64 hwprobe_misaligned(const struct cpumask *cpus) +{ + return RISCV_HWPROBE_MISALIGNED_EMULATED; +} +#elif defined(CONFIG_RISCV_SLOW_UNALIGNED_ACCESS) +static u64 hwprobe_misaligned(const struct cpumask *cpus) +{ + return RISCV_HWPROBE_MISALIGNED_SLOW; +} +#elif defined(CONFIG_RISCV_EFFICIENT_UNALIGNED_ACCESS) +static u64 hwprobe_misaligned(const struct cpumask *cpus) +{ + return RISCV_HWPROBE_MISALIGNED_FAST; +} +#elif defined(CONFIG_RISCV_UNSUPPORTED_UNALIGNED_ACCESS) +static u64 hwprobe_misaligned(const struct cpumask *cpus) +{ + return RISCV_HWPROBE_MISALIGNED_UNSUPPORTED; +} +#endif static void hwprobe_one_pair(struct riscv_hwprobe *pair, const struct cpumask *cpus) diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c index 8ded225e8c5b..ba6763dd9895 100644 --- a/arch/riscv/kernel/traps_misaligned.c +++ b/arch/riscv/kernel/traps_misaligned.c @@ -398,8 +398,6 @@ union reg_data { u64 data_u64; }; -static bool unaligned_ctl __read_mostly; - /* sysctl hooks */ int unaligned_enabled __read_mostly = 1; /* Enabled by default */ @@ -413,7 +411,9 @@ int handle_misaligned_load(struct pt_regs *regs) perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr); +#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS *this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_EMULATED; +#endif if (!unaligned_enabled) return -1; @@ -595,53 +595,3 @@ int handle_misaligned_store(struct pt_regs *regs) return 0; } - -bool check_unaligned_access_emulated(int cpu) -{ - long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu); - unsigned long tmp_var, tmp_val; - bool misaligned_emu_detected; - - *mas_ptr = RISCV_HWPROBE_MISALIGNED_UNKNOWN; - - __asm__ __volatile__ ( - " "REG_L" %[tmp], 1(%[ptr])\n" - : [tmp] "=r" (tmp_val) : [ptr] "r" (&tmp_var) : "memory"); - - misaligned_emu_detected = (*mas_ptr == RISCV_HWPROBE_MISALIGNED_EMULATED); - /* - * If unaligned_ctl is already set, this means that we detected that all - * CPUS uses emulated misaligned access at boot time. If that changed - * when hotplugging the new cpu, this is something we don't handle. - */ - if (unlikely(unaligned_ctl && !misaligned_emu_detected)) { - pr_crit("CPU misaligned accesses non homogeneous (expected all emulated)\n"); - while (true) - cpu_relax(); - } - - return misaligned_emu_detected; -} - -void unaligned_emulation_finish(void) -{ - int cpu; - - /* - * We can only support PR_UNALIGN controls if all CPUs have misaligned - * accesses emulated since tasks requesting such control can run on any - * CPU. - */ - for_each_present_cpu(cpu) { - if (per_cpu(misaligned_access_speed, cpu) != - RISCV_HWPROBE_MISALIGNED_EMULATED) { - return; - } - } - unaligned_ctl = true; -} - -bool unaligned_ctl_available(void) -{ - return unaligned_ctl; -} -- 2.43.2
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