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authorNicholas Piggin <npiggin@gmail.com>2020-06-25 15:34:03 +1000
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2020-06-30 17:18:56 -0400
commitb23d7a5f4a07af02343cdd28fe1f7488bac3afda (patch)
treec775987b3e84915ec4c22a410f65c8c145ee70ce /kernel/trace/ring_buffer.c
parent10464b4aa605ef93c937452f442e74cc0a4a6ceb (diff)
downloadlinux-b23d7a5f4a07af02343cdd28fe1f7488bac3afda.tar.bz2
ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU
On a 144 thread system, `perf ftrace` takes about 20 seconds to start up, due to calling synchronize_rcu() for each CPU. cat /proc/108560/stack 0xc0003e7eb336f470 __switch_to+0x2e0/0x480 __wait_rcu_gp+0x20c/0x220 synchronize_rcu+0x9c/0xc0 ring_buffer_reset_cpu+0x88/0x2e0 tracing_reset_online_cpus+0x84/0xe0 tracing_open+0x1d4/0x1f0 On a system with 10x more threads, it starts to become an annoyance. Batch these up so we disable all the per-cpu buffers first, then synchronize_rcu() once, then reset each of the buffers. This brings the time down to about 0.5s. Link: https://lkml.kernel.org/r/20200625053403.2386972-1-npiggin@gmail.com Tested-by: Anton Blanchard <anton@ozlabs.org> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/ring_buffer.c')
-rw-r--r--kernel/trace/ring_buffer.c85
1 files changed, 71 insertions, 14 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 802bb38d9c81..ed1941304f69 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -270,6 +270,9 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define for_each_buffer_cpu(buffer, cpu) \
for_each_cpu(cpu, buffer->cpumask)
+#define for_each_online_buffer_cpu(buffer, cpu) \
+ for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
+
#define TS_SHIFT 27
#define TS_MASK ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST (~TS_MASK)
@@ -4790,6 +4793,26 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
rb_head_page_activate(cpu_buffer);
}
+/* Must have disabled the cpu buffer then done a synchronize_rcu */
+static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+ if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
+ goto out;
+
+ arch_spin_lock(&cpu_buffer->lock);
+
+ rb_reset_cpu(cpu_buffer);
+
+ arch_spin_unlock(&cpu_buffer->lock);
+
+ out:
+ raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+}
+
/**
* ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
@@ -4798,7 +4821,6 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
- unsigned long flags;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
@@ -4809,24 +4831,42 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
/* Make sure all commits have finished */
synchronize_rcu();
- raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+ reset_disabled_cpu_buffer(cpu_buffer);
- if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
- goto out;
+ atomic_dec(&cpu_buffer->record_disabled);
+ atomic_dec(&cpu_buffer->resize_disabled);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
- arch_spin_lock(&cpu_buffer->lock);
+/**
+ * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
+ * @buffer: The ring buffer to reset a per cpu buffer of
+ * @cpu: The CPU buffer to be reset
+ */
+void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+ int cpu;
- rb_reset_cpu(cpu_buffer);
+ for_each_online_buffer_cpu(buffer, cpu) {
+ cpu_buffer = buffer->buffers[cpu];
- arch_spin_unlock(&cpu_buffer->lock);
+ atomic_inc(&cpu_buffer->resize_disabled);
+ atomic_inc(&cpu_buffer->record_disabled);
+ }
- out:
- raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ /* Make sure all commits have finished */
+ synchronize_rcu();
- atomic_dec(&cpu_buffer->record_disabled);
- atomic_dec(&cpu_buffer->resize_disabled);
+ for_each_online_buffer_cpu(buffer, cpu) {
+ cpu_buffer = buffer->buffers[cpu];
+
+ reset_disabled_cpu_buffer(cpu_buffer);
+
+ atomic_dec(&cpu_buffer->record_disabled);
+ atomic_dec(&cpu_buffer->resize_disabled);
+ }
}
-EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
/**
* ring_buffer_reset - reset a ring buffer
@@ -4834,10 +4874,27 @@ EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
*/
void ring_buffer_reset(struct trace_buffer *buffer)
{
+ struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
- for_each_buffer_cpu(buffer, cpu)
- ring_buffer_reset_cpu(buffer, cpu);
+ for_each_buffer_cpu(buffer, cpu) {
+ cpu_buffer = buffer->buffers[cpu];
+
+ atomic_inc(&cpu_buffer->resize_disabled);
+ atomic_inc(&cpu_buffer->record_disabled);
+ }
+
+ /* Make sure all commits have finished */
+ synchronize_rcu();
+
+ for_each_buffer_cpu(buffer, cpu) {
+ cpu_buffer = buffer->buffers[cpu];
+
+ reset_disabled_cpu_buffer(cpu_buffer);
+
+ atomic_dec(&cpu_buffer->record_disabled);
+ atomic_dec(&cpu_buffer->resize_disabled);
+ }
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);