[PATCH 04/16] ring-buffer: remove unneeded get_online_cpus

Steven Rostedt
2009-03-13T02:41:22Z

[-- Attachment #1: 0004-ring-buffer-remove-unneeded-get_online_cpus.patch --]
[-- Type: text/plain, Size: 7683 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

Impact: speed up and remove possible races

The get_online_cpus was added to the ring buffer because the original
design would free the ring buffer on a CPU that was being taken
off line. The final design kept the ring buffer around even when the
CPU was taken off line. This is to allow a user to still read the
information on that ring buffer.

Most of the get_online_cpus are no longer needed since the ring buffer will
not disappear from the use cases.

Reported-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
kernel/trace/ring_buffer.c | 90 +++++++-------------------------------------
1 files changed, 14 insertions(+), 76 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 035b56c..2c36be9 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1561,15 +1561,11 @@ void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;

- get_online_cpus();
-
if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return;

cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->record_disabled);
- out:
- put_online_cpus();
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);

@@ -1585,15 +1581,11 @@ void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;

- get_online_cpus();
-
if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return;

cpu_buffer = buffer->buffers[cpu];
atomic_dec(&cpu_buffer->record_disabled);
- out:
- put_online_cpus();
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);

@@ -1605,17 +1597,13 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
- unsigned long ret = 0;
-
- get_online_cpus();
+ unsigned long ret;

if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return 0;

cpu_buffer = buffer->buffers[cpu];
ret = cpu_buffer->entries;
- out:
- put_online_cpus();

return ret;
}
@@ -1629,17 +1617,13 @@ EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
- unsigned long ret = 0;
-
- get_online_cpus();
+ unsigned long ret;

if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return 0;

cpu_buffer = buffer->buffers[cpu];
ret = cpu_buffer->overrun;
- out:
- put_online_cpus();

return ret;
}
@@ -1658,16 +1642,12 @@ unsigned long ring_buffer_entries(struct ring_buffer *buffer)
unsigned long entries = 0;
int cpu;

- get_online_cpus();
-
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
entries += cpu_buffer->entries;
}

- put_online_cpus();
-
return entries;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries);
@@ -1685,16 +1665,12 @@ unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
unsigned long overruns = 0;
int cpu;

- get_online_cpus();
-
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
overruns += cpu_buffer->overrun;
}

- put_online_cpus();
-
return overruns;
}
EXPORT_SYMBOL_GPL(ring_buffer_overruns);
@@ -2093,21 +2069,16 @@ struct ring_buffer_event *
ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
- struct ring_buffer_event *event = NULL;
+ struct ring_buffer_event *event;
unsigned long flags;

- get_online_cpus();
-
if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return NULL;

spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_buffer_peek(buffer, cpu, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

- out:
- put_online_cpus();
-
return event;
}

@@ -2189,17 +2160,15 @@ struct ring_buffer_iter *
ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
- struct ring_buffer_iter *iter = NULL;
+ struct ring_buffer_iter *iter;
unsigned long flags;

- get_online_cpus();
-
if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return NULL;

iter = kmalloc(sizeof(*iter), GFP_KERNEL);
if (!iter)
- goto out;
+ return NULL;

cpu_buffer = buffer->buffers[cpu];

@@ -2214,9 +2183,6 @@ ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
__raw_spin_unlock(&cpu_buffer->lock);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

- out:
- put_online_cpus();
-
return iter;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_start);
@@ -2309,13 +2275,9 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
unsigned long flags;
- int resched;
-
- /* Can't use get_online_cpus because this can be in atomic */
- resched = ftrace_preempt_disable();

if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return;

spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

@@ -2326,8 +2288,6 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
__raw_spin_unlock(&cpu_buffer->lock);

spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
- out:
- ftrace_preempt_enable(resched);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);

@@ -2337,16 +2297,10 @@ EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
*/
void ring_buffer_reset(struct ring_buffer *buffer)
{
- int resched;
int cpu;

- /* Can't use get_online_cpus because this can be in atomic */
- resched = ftrace_preempt_disable();
-
for_each_buffer_cpu(buffer, cpu)
ring_buffer_reset_cpu(buffer, cpu);
-
- ftrace_preempt_enable(resched);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);

@@ -2359,8 +2313,6 @@ int ring_buffer_empty(struct ring_buffer *buffer)
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;

- get_online_cpus();
-
/* yes this is racy, but if you don't like the race, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
@@ -2368,8 +2320,6 @@ int ring_buffer_empty(struct ring_buffer *buffer)
return 0;
}

- put_online_cpus();
-
return 1;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty);
@@ -2382,18 +2332,14 @@ EXPORT_SYMBOL_GPL(ring_buffer_empty);
int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
- int ret = 1;
-
- get_online_cpus();
+ int ret;

if (!cpumask_test_cpu(cpu, buffer->cpumask))
- goto out;
+ return 1;

cpu_buffer = buffer->buffers[cpu];
ret = rb_per_cpu_empty(cpu_buffer);

- out:
- put_online_cpus();

return ret;
}
@@ -2416,8 +2362,6 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
struct ring_buffer_per_cpu *cpu_buffer_b;
int ret = -EINVAL;

- get_online_cpus();
-
if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
!cpumask_test_cpu(cpu, buffer_b->cpumask))
goto out;
@@ -2466,8 +2410,6 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,

ret = 0;
out:
- put_online_cpus();
-
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
@@ -2583,8 +2525,6 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
u64 save_timestamp;
int ret = -1;

- get_online_cpus();
-
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;

@@ -2681,8 +2621,6 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

out:
- put_online_cpus();
-
return ret;
}

--
1.6.1.3

--