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-rw-r--r--arch/riscv/kernel/unaligned_access_speed.c281
1 files changed, 281 insertions, 0 deletions
diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
new file mode 100644
index 000000000000..a9a6bcb02acf
--- /dev/null
+++ b/arch/riscv/kernel/unaligned_access_speed.c
@@ -0,0 +1,281 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2024 Rivos Inc.
+ */
+
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/jump_label.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/types.h>
+#include <asm/cpufeature.h>
+#include <asm/hwprobe.h>
+
+#include "copy-unaligned.h"
+
+#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)
+
+DEFINE_PER_CPU(long, misaligned_access_speed);
+
+#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
+static cpumask_t fast_misaligned_access;
+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 (per_cpu(misaligned_access_speed, cpu) != RISCV_HWPROBE_MISALIGNED_UNKNOWN)
+ 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 speed on all CPUs present at boot in parallel. */
+static int check_unaligned_access_speed_all_cpus(void)
+{
+ unsigned int cpu;
+ unsigned int cpu_count = num_possible_cpus();
+ struct page **bufs = kcalloc(cpu_count, sizeof(*bufs), 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:
+ for_each_cpu(cpu, cpu_online_mask) {
+ if (bufs[cpu])
+ __free_pages(bufs[cpu], MISALIGNED_BUFFER_ORDER);
+ }
+
+ kfree(bufs);
+ return 0;
+}
+
+static int check_unaligned_access_all_cpus(void)
+{
+ bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
+
+ if (!all_cpus_emulated)
+ return check_unaligned_access_speed_all_cpus();
+
+ return 0;
+}
+#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
+static int check_unaligned_access_all_cpus(void)
+{
+ check_unaligned_access_emulated_all_cpus();
+
+ return 0;
+}
+#endif
+
+arch_initcall(check_unaligned_access_all_cpus);