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![Robert Richter](/assets/img/avatar_default.png)
Special events such as task or context switches are marked with an escape code in the cpu buffer followed by an event code or a task identifier. There is one escape code per event. To make escape sequences also available for data samples the internal cpu buffer format must be changed. The current implementation does not allow the extension of event codes since this would lead to collisions with the task identifiers. To avoid this, this patch introduces an event mask that allows the storage of multiple events with one escape code. Now, task identifiers are stored in the data section of the sample. The implementation also allows the usage of custom data in a sample. As a side effect the new code is much more readable and easier to understand. Signed-off-by: Robert Richter <robert.richter@amd.com>
450 lines
11 KiB
C
450 lines
11 KiB
C
/**
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* @file cpu_buffer.c
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*
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* @remark Copyright 2002-2009 OProfile authors
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* @remark Read the file COPYING
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*
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* @author John Levon <levon@movementarian.org>
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* @author Barry Kasindorf <barry.kasindorf@amd.com>
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* @author Robert Richter <robert.richter@amd.com>
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*
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* Each CPU has a local buffer that stores PC value/event
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* pairs. We also log context switches when we notice them.
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* Eventually each CPU's buffer is processed into the global
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* event buffer by sync_buffer().
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*
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* We use a local buffer for two reasons: an NMI or similar
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* interrupt cannot synchronise, and high sampling rates
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* would lead to catastrophic global synchronisation if
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* a global buffer was used.
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*/
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#include <linux/sched.h>
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#include <linux/oprofile.h>
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#include <linux/vmalloc.h>
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#include <linux/errno.h>
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#include "event_buffer.h"
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#include "cpu_buffer.h"
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#include "buffer_sync.h"
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#include "oprof.h"
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#define OP_BUFFER_FLAGS 0
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/*
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* Read and write access is using spin locking. Thus, writing to the
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* buffer by NMI handler (x86) could occur also during critical
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* sections when reading the buffer. To avoid this, there are 2
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* buffers for independent read and write access. Read access is in
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* process context only, write access only in the NMI handler. If the
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* read buffer runs empty, both buffers are swapped atomically. There
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* is potentially a small window during swapping where the buffers are
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* disabled and samples could be lost.
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*
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* Using 2 buffers is a little bit overhead, but the solution is clear
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* and does not require changes in the ring buffer implementation. It
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* can be changed to a single buffer solution when the ring buffer
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* access is implemented as non-locking atomic code.
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*/
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static struct ring_buffer *op_ring_buffer_read;
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static struct ring_buffer *op_ring_buffer_write;
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DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);
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static void wq_sync_buffer(struct work_struct *work);
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#define DEFAULT_TIMER_EXPIRE (HZ / 10)
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static int work_enabled;
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unsigned long oprofile_get_cpu_buffer_size(void)
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{
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return oprofile_cpu_buffer_size;
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}
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void oprofile_cpu_buffer_inc_smpl_lost(void)
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{
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struct oprofile_cpu_buffer *cpu_buf
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= &__get_cpu_var(cpu_buffer);
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cpu_buf->sample_lost_overflow++;
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}
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void free_cpu_buffers(void)
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{
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if (op_ring_buffer_read)
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ring_buffer_free(op_ring_buffer_read);
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op_ring_buffer_read = NULL;
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if (op_ring_buffer_write)
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ring_buffer_free(op_ring_buffer_write);
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op_ring_buffer_write = NULL;
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}
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int alloc_cpu_buffers(void)
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{
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int i;
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unsigned long buffer_size = oprofile_cpu_buffer_size;
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op_ring_buffer_read = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
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if (!op_ring_buffer_read)
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goto fail;
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op_ring_buffer_write = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
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if (!op_ring_buffer_write)
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goto fail;
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for_each_possible_cpu(i) {
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struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
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b->last_task = NULL;
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b->last_is_kernel = -1;
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b->tracing = 0;
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b->buffer_size = buffer_size;
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b->sample_received = 0;
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b->sample_lost_overflow = 0;
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b->backtrace_aborted = 0;
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b->sample_invalid_eip = 0;
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b->cpu = i;
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INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
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}
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return 0;
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fail:
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free_cpu_buffers();
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return -ENOMEM;
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}
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void start_cpu_work(void)
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{
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int i;
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work_enabled = 1;
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for_each_online_cpu(i) {
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struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
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/*
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* Spread the work by 1 jiffy per cpu so they dont all
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* fire at once.
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*/
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schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
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}
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}
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void end_cpu_work(void)
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{
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int i;
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work_enabled = 0;
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for_each_online_cpu(i) {
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struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
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cancel_delayed_work(&b->work);
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}
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flush_scheduled_work();
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}
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/*
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* This function prepares the cpu buffer to write a sample.
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*
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* Struct op_entry is used during operations on the ring buffer while
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* struct op_sample contains the data that is stored in the ring
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* buffer. Struct entry can be uninitialized. The function reserves a
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* data array that is specified by size. Use
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* op_cpu_buffer_write_commit() after preparing the sample. In case of
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* errors a null pointer is returned, otherwise the pointer to the
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* sample.
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*
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*/
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struct op_sample
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*op_cpu_buffer_write_reserve(struct op_entry *entry, unsigned long size)
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{
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entry->event = ring_buffer_lock_reserve
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(op_ring_buffer_write, sizeof(struct op_sample) +
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size * sizeof(entry->sample->data[0]), &entry->irq_flags);
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if (entry->event)
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entry->sample = ring_buffer_event_data(entry->event);
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else
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entry->sample = NULL;
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if (!entry->sample)
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return NULL;
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entry->size = size;
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entry->data = entry->sample->data;
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return entry->sample;
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}
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int op_cpu_buffer_write_commit(struct op_entry *entry)
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{
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return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event,
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entry->irq_flags);
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}
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struct op_sample *op_cpu_buffer_read_entry(struct op_entry *entry, int cpu)
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{
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struct ring_buffer_event *e;
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e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
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if (e)
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goto event;
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if (ring_buffer_swap_cpu(op_ring_buffer_read,
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op_ring_buffer_write,
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cpu))
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return NULL;
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e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
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if (e)
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goto event;
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return NULL;
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event:
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entry->event = e;
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entry->sample = ring_buffer_event_data(e);
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entry->size = (ring_buffer_event_length(e) - sizeof(struct op_sample))
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/ sizeof(entry->sample->data[0]);
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entry->data = entry->sample->data;
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return entry->sample;
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}
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unsigned long op_cpu_buffer_entries(int cpu)
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{
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return ring_buffer_entries_cpu(op_ring_buffer_read, cpu)
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+ ring_buffer_entries_cpu(op_ring_buffer_write, cpu);
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}
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static int
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op_add_code(struct oprofile_cpu_buffer *cpu_buf, unsigned long backtrace,
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int is_kernel, struct task_struct *task)
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{
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struct op_entry entry;
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struct op_sample *sample;
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unsigned long flags;
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int size;
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flags = 0;
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if (backtrace)
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flags |= TRACE_BEGIN;
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/* notice a switch from user->kernel or vice versa */
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is_kernel = !!is_kernel;
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if (cpu_buf->last_is_kernel != is_kernel) {
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cpu_buf->last_is_kernel = is_kernel;
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flags |= KERNEL_CTX_SWITCH;
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if (is_kernel)
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flags |= IS_KERNEL;
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}
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/* notice a task switch */
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if (cpu_buf->last_task != task) {
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cpu_buf->last_task = task;
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flags |= USER_CTX_SWITCH;
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}
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if (!flags)
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/* nothing to do */
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return 0;
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if (flags & USER_CTX_SWITCH)
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size = 1;
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else
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size = 0;
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sample = op_cpu_buffer_write_reserve(&entry, size);
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if (!sample)
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return -ENOMEM;
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sample->eip = ESCAPE_CODE;
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sample->event = flags;
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if (size)
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sample->data[0] = (unsigned long)task;
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op_cpu_buffer_write_commit(&entry);
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return 0;
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}
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static inline int
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op_add_sample(struct oprofile_cpu_buffer *cpu_buf,
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unsigned long pc, unsigned long event)
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{
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struct op_entry entry;
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struct op_sample *sample;
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sample = op_cpu_buffer_write_reserve(&entry, 0);
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if (!sample)
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return -ENOMEM;
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sample->eip = pc;
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sample->event = event;
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return op_cpu_buffer_write_commit(&entry);
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}
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/*
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* This must be safe from any context.
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*
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* is_kernel is needed because on some architectures you cannot
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* tell if you are in kernel or user space simply by looking at
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* pc. We tag this in the buffer by generating kernel enter/exit
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* events whenever is_kernel changes
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*/
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static int
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log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
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unsigned long backtrace, int is_kernel, unsigned long event)
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{
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cpu_buf->sample_received++;
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if (pc == ESCAPE_CODE) {
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cpu_buf->sample_invalid_eip++;
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return 0;
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}
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if (op_add_code(cpu_buf, backtrace, is_kernel, current))
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goto fail;
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if (op_add_sample(cpu_buf, pc, event))
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goto fail;
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return 1;
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fail:
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cpu_buf->sample_lost_overflow++;
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return 0;
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}
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static inline void oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
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{
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cpu_buf->tracing = 1;
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}
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static inline void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
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{
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cpu_buf->tracing = 0;
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}
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static inline void
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__oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
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unsigned long event, int is_kernel)
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{
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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unsigned long backtrace = oprofile_backtrace_depth;
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/*
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* if log_sample() fail we can't backtrace since we lost the
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* source of this event
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*/
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if (!log_sample(cpu_buf, pc, backtrace, is_kernel, event))
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/* failed */
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return;
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if (!backtrace)
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return;
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oprofile_begin_trace(cpu_buf);
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oprofile_ops.backtrace(regs, backtrace);
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oprofile_end_trace(cpu_buf);
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}
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void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
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unsigned long event, int is_kernel)
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{
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__oprofile_add_ext_sample(pc, regs, event, is_kernel);
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}
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void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
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{
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int is_kernel = !user_mode(regs);
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unsigned long pc = profile_pc(regs);
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__oprofile_add_ext_sample(pc, regs, event, is_kernel);
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}
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#ifdef CONFIG_OPROFILE_IBS
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void oprofile_add_ibs_sample(struct pt_regs * const regs,
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unsigned int * const ibs_sample, int ibs_code)
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{
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int is_kernel = !user_mode(regs);
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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int fail = 0;
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cpu_buf->sample_received++;
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/* backtraces disabled for ibs */
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fail = fail || op_add_code(cpu_buf, 0, is_kernel, current);
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fail = fail || op_add_sample(cpu_buf, ESCAPE_CODE, ibs_code);
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fail = fail || op_add_sample(cpu_buf, ibs_sample[0], ibs_sample[1]);
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fail = fail || op_add_sample(cpu_buf, ibs_sample[2], ibs_sample[3]);
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fail = fail || op_add_sample(cpu_buf, ibs_sample[4], ibs_sample[5]);
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if (ibs_code == IBS_OP_BEGIN) {
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fail = fail || op_add_sample(cpu_buf, ibs_sample[6], ibs_sample[7]);
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fail = fail || op_add_sample(cpu_buf, ibs_sample[8], ibs_sample[9]);
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fail = fail || op_add_sample(cpu_buf, ibs_sample[10], ibs_sample[11]);
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}
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if (fail)
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cpu_buf->sample_lost_overflow++;
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}
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#endif
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void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
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{
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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log_sample(cpu_buf, pc, 0, is_kernel, event);
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}
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void oprofile_add_trace(unsigned long pc)
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{
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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if (!cpu_buf->tracing)
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return;
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/*
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* broken frame can give an eip with the same value as an
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* escape code, abort the trace if we get it
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*/
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if (pc == ESCAPE_CODE)
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goto fail;
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if (op_add_sample(cpu_buf, pc, 0))
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goto fail;
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return;
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fail:
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cpu_buf->tracing = 0;
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cpu_buf->backtrace_aborted++;
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return;
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}
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/*
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* This serves to avoid cpu buffer overflow, and makes sure
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* the task mortuary progresses
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*
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* By using schedule_delayed_work_on and then schedule_delayed_work
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* we guarantee this will stay on the correct cpu
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*/
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static void wq_sync_buffer(struct work_struct *work)
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{
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struct oprofile_cpu_buffer *b =
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container_of(work, struct oprofile_cpu_buffer, work.work);
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if (b->cpu != smp_processor_id()) {
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printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
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smp_processor_id(), b->cpu);
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if (!cpu_online(b->cpu)) {
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cancel_delayed_work(&b->work);
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return;
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}
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}
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sync_buffer(b->cpu);
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/* don't re-add the work if we're shutting down */
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if (work_enabled)
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schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
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}
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