aboutsummaryrefslogtreecommitdiff
path: root/kernel
diff options
context:
space:
mode:
authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2015-05-21 17:39:29 -0400
committerSasha Levin <sasha.levin@oracle.com>2016-06-06 19:11:04 -0400
commit4baf9733a655b71db7b436484dfdc04566c3a5a3 (patch)
tree0511756f13fd569a4425b87af86bf461edb6c8c5 /kernel
parentde66b0f01581ae7780938e439e87b4c446106b3d (diff)
downloadlinux-linaro-stable-4baf9733a655b71db7b436484dfdc04566c3a5a3.tar.gz
ring-buffer: Add unlikelys to make fast path the default
[ Upstream commit 3205f8063b6cc54b20d5080fb79dfcbd9c39e93d ] I was running the trace_event benchmark and noticed that the times to record a trace_event was all over the place. I looked at the assembly of the ring_buffer_lock_reserver() and saw this: <ring_buffer_lock_reserve>: 31 c0 xor %eax,%eax 48 83 3d 76 47 bd 00 cmpq $0x1,0xbd4776(%rip) # ffffffff81d10d60 <ring_buffer_flags> 01 55 push %rbp 48 89 e5 mov %rsp,%rbp 75 1d jne ffffffff8113c60d <ring_buffer_lock_reserve+0x2d> 65 ff 05 69 e3 ec 7e incl %gs:0x7eece369(%rip) # a960 <__preempt_count> 8b 47 08 mov 0x8(%rdi),%eax 85 c0 test %eax,%eax +---- 74 12 je ffffffff8113c610 <ring_buffer_lock_reserve+0x30> | 65 ff 0d 5b e3 ec 7e decl %gs:0x7eece35b(%rip) # a960 <__preempt_count> | 0f 84 85 00 00 00 je ffffffff8113c690 <ring_buffer_lock_reserve+0xb0> | 31 c0 xor %eax,%eax | 5d pop %rbp | c3 retq | 90 nop +---> 65 44 8b 05 48 e3 ec mov %gs:0x7eece348(%rip),%r8d # a960 <__preempt_count> 7e 41 81 e0 ff ff ff 7f and $0x7fffffff,%r8d b0 08 mov $0x8,%al 65 8b 0d 58 36 ed 7e mov %gs:0x7eed3658(%rip),%ecx # fc80 <current_context> 41 f7 c0 00 ff 1f 00 test $0x1fff00,%r8d 74 1e je ffffffff8113c64f <ring_buffer_lock_reserve+0x6f> 41 f7 c0 00 00 10 00 test $0x100000,%r8d b0 01 mov $0x1,%al 75 13 jne ffffffff8113c64f <ring_buffer_lock_reserve+0x6f> 41 81 e0 00 00 0f 00 and $0xf0000,%r8d 49 83 f8 01 cmp $0x1,%r8 19 c0 sbb %eax,%eax 83 e0 02 and $0x2,%eax 83 c0 02 add $0x2,%eax 85 c8 test %ecx,%eax 75 ab jne ffffffff8113c5fe <ring_buffer_lock_reserve+0x1e> 09 c8 or %ecx,%eax 65 89 05 24 36 ed 7e mov %eax,%gs:0x7eed3624(%rip) # fc80 <current_context> The arrow is the fast path. After adding the unlikely's, the fast path looks a bit better: <ring_buffer_lock_reserve>: 31 c0 xor %eax,%eax 48 83 3d 76 47 bd 00 cmpq $0x1,0xbd4776(%rip) # ffffffff81d10d60 <ring_buffer_flags> 01 55 push %rbp 48 89 e5 mov %rsp,%rbp 75 7b jne ffffffff8113c66b <ring_buffer_lock_reserve+0x8b> 65 ff 05 69 e3 ec 7e incl %gs:0x7eece369(%rip) # a960 <__preempt_count> 8b 47 08 mov 0x8(%rdi),%eax 85 c0 test %eax,%eax 0f 85 9f 00 00 00 jne ffffffff8113c6a1 <ring_buffer_lock_reserve+0xc1> 65 8b 0d 57 e3 ec 7e mov %gs:0x7eece357(%rip),%ecx # a960 <__preempt_count> 81 e1 ff ff ff 7f and $0x7fffffff,%ecx b0 08 mov $0x8,%al 65 8b 15 68 36 ed 7e mov %gs:0x7eed3668(%rip),%edx # fc80 <current_context> f7 c1 00 ff 1f 00 test $0x1fff00,%ecx 75 50 jne ffffffff8113c670 <ring_buffer_lock_reserve+0x90> 85 d0 test %edx,%eax 75 7d jne ffffffff8113c6a1 <ring_buffer_lock_reserve+0xc1> 09 d0 or %edx,%eax 65 89 05 53 36 ed 7e mov %eax,%gs:0x7eed3653(%rip) # fc80 <current_context> 65 8b 05 fc da ec 7e mov %gs:0x7eecdafc(%rip),%eax # a130 <cpu_number> 89 c2 mov %eax,%edx Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/ring_buffer.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 0fc5cfedcc8c..0b6b66720e2b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2749,23 +2749,23 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
/* If we are tracing schedule, we don't want to recurse */
preempt_disable_notrace();
- if (atomic_read(&buffer->record_disabled))
+ if (unlikely(atomic_read(&buffer->record_disabled)))
goto out_nocheck;
- if (trace_recursive_lock())
+ if (unlikely(trace_recursive_lock()))
goto out_nocheck;
cpu = raw_smp_processor_id();
- if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
goto out;
cpu_buffer = buffer->buffers[cpu];
- if (atomic_read(&cpu_buffer->record_disabled))
+ if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
goto out;
- if (length > BUF_MAX_DATA_SIZE)
+ if (unlikely(length > BUF_MAX_DATA_SIZE))
goto out;
event = rb_reserve_next_event(buffer, cpu_buffer, length);