/** * @file cpu_buffer.c * * @remark Copyright 2002 OProfile authors * @remark Read the file COPYING * * @author John Levon <levon@movementarian.org> * * Each CPU has a local buffer that stores PC value/event * pairs. We also log context switches when we notice them. * Eventually each CPU's buffer is processed into the global * event buffer by sync_buffer(). * * We use a local buffer for two reasons: an NMI or similar * interrupt cannot synchronise, and high sampling rates * would lead to catastrophic global synchronisation if * a global buffer was used. */ #include <linux/sched.h> #include <linux/oprofile.h> #include <linux/vmalloc.h> #include <linux/errno.h> #include "event_buffer.h" #include "cpu_buffer.h" #include "buffer_sync.h" #include "oprof.h" struct oprofile_cpu_buffer cpu_buffer[NR_CPUS] __cacheline_aligned; static void wq_sync_buffer(struct work_struct *work); #define DEFAULT_TIMER_EXPIRE (HZ / 10) static int work_enabled; void free_cpu_buffers(void) { int i; for_each_online_cpu(i) vfree(cpu_buffer[i].buffer); } int alloc_cpu_buffers(void) { int i; unsigned long buffer_size = fs_cpu_buffer_size; for_each_online_cpu(i) { struct oprofile_cpu_buffer * b = &cpu_buffer[i]; b->buffer = vmalloc_node(sizeof(struct op_sample) * buffer_size, cpu_to_node(i)); if (!b->buffer) goto fail; b->last_task = NULL; b->last_is_kernel = -1; b->tracing = 0; b->buffer_size = buffer_size; b->tail_pos = 0; b->head_pos = 0; b->sample_received = 0; b->sample_lost_overflow = 0; b->cpu = i; INIT_DELAYED_WORK(&b->work, wq_sync_buffer); } return 0; fail: free_cpu_buffers(); return -ENOMEM; } void start_cpu_work(void) { int i; work_enabled = 1; for_each_online_cpu(i) { struct oprofile_cpu_buffer * b = &cpu_buffer[i]; /* * Spread the work by 1 jiffy per cpu so they dont all * fire at once. */ schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i); } } void end_cpu_work(void) { int i; work_enabled = 0; for_each_online_cpu(i) { struct oprofile_cpu_buffer * b = &cpu_buffer[i]; cancel_delayed_work(&b->work); } flush_scheduled_work(); } /* Resets the cpu buffer to a sane state. */ void cpu_buffer_reset(struct oprofile_cpu_buffer * cpu_buf) { /* reset these to invalid values; the next sample * collected will populate the buffer with proper * values to initialize the buffer */ cpu_buf->last_is_kernel = -1; cpu_buf->last_task = NULL; } /* compute number of available slots in cpu_buffer queue */ static unsigned long nr_available_slots(struct oprofile_cpu_buffer const * b) { unsigned long head = b->head_pos; unsigned long tail = b->tail_pos; if (tail > head) return (tail - head) - 1; return tail + (b->buffer_size - head) - 1; } static void increment_head(struct oprofile_cpu_buffer * b) { unsigned long new_head = b->head_pos + 1; /* Ensure anything written to the slot before we * increment is visible */ wmb(); if (new_head < b->buffer_size) b->head_pos = new_head; else b->head_pos = 0; } static inline void add_sample(struct oprofile_cpu_buffer * cpu_buf, unsigned long pc, unsigned long event) { struct op_sample * entry = &cpu_buf->buffer[cpu_buf->head_pos]; entry->eip = pc; entry->event = event; increment_head(cpu_buf); } static inline void add_code(struct oprofile_cpu_buffer * buffer, unsigned long value) { add_sample(buffer, ESCAPE_CODE, value); } /* This must be safe from any context. It's safe writing here * because of the head/tail separation of the writer and reader * of the CPU buffer. * * is_kernel is needed because on some architectures you cannot * tell if you are in kernel or user space simply by looking at * pc. We tag this in the buffer by generating kernel enter/exit * events whenever is_kernel changes */ static int log_sample(struct oprofile_cpu_buffer * cpu_buf, unsigned long pc, int is_kernel, unsigned long event) { struct task_struct * task; cpu_buf->sample_received++; if (nr_available_slots(cpu_buf) < 3) { cpu_buf->sample_lost_overflow++; return 0; } is_kernel = !!is_kernel; task = current; /* notice a switch from user->kernel or vice versa */ if (cpu_buf->last_is_kernel != is_kernel) { cpu_buf->last_is_kernel = is_kernel; add_code(cpu_buf, is_kernel); } /* notice a task switch */ if (cpu_buf->last_task != task) { cpu_buf->last_task = task; add_code(cpu_buf, (unsigned long)task); } add_sample(cpu_buf, pc, event); return 1; } static int oprofile_begin_trace(struct oprofile_cpu_buffer * cpu_buf) { if (nr_available_slots(cpu_buf) < 4) { cpu_buf->sample_lost_overflow++; return 0; } add_code(cpu_buf, CPU_TRACE_BEGIN); cpu_buf->tracing = 1; return 1; } static void oprofile_end_trace(struct oprofile_cpu_buffer * cpu_buf) { cpu_buf->tracing = 0; } void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs, unsigned long event, int is_kernel) { struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; if (!backtrace_depth) { log_sample(cpu_buf, pc, is_kernel, event); return; } if (!oprofile_begin_trace(cpu_buf)) return; /* if log_sample() fail we can't backtrace since we lost the source * of this event */ if (log_sample(cpu_buf, pc, is_kernel, event)) oprofile_ops.backtrace(regs, backtrace_depth); oprofile_end_trace(cpu_buf); } void oprofile_add_sample(struct pt_regs * const regs, unsigned long event) { int is_kernel = !user_mode(regs); unsigned long pc = profile_pc(regs); oprofile_add_ext_sample(pc, regs, event, is_kernel); } void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event) { struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; log_sample(cpu_buf, pc, is_kernel, event); } void oprofile_add_trace(unsigned long pc) { struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; if (!cpu_buf->tracing) return; if (nr_available_slots(cpu_buf) < 1) { cpu_buf->tracing = 0; cpu_buf->sample_lost_overflow++; return; } /* broken frame can give an eip with the same value as an escape code, * abort the trace if we get it */ if (pc == ESCAPE_CODE) { cpu_buf->tracing = 0; cpu_buf->backtrace_aborted++; return; } add_sample(cpu_buf, pc, 0); } /* * This serves to avoid cpu buffer overflow, and makes sure * the task mortuary progresses * * By using schedule_delayed_work_on and then schedule_delayed_work * we guarantee this will stay on the correct cpu */ static void wq_sync_buffer(struct work_struct *work) { struct oprofile_cpu_buffer * b = container_of(work, struct oprofile_cpu_buffer, work.work); if (b->cpu != smp_processor_id()) { printk("WQ on CPU%d, prefer CPU%d\n", smp_processor_id(), b->cpu); } sync_buffer(b->cpu); /* don't re-add the work if we're shutting down */ if (work_enabled) schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE); }