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author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2015-05-21 17:39:29 -0400 |
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committer | Steven Rostedt <rostedt@goodmis.org> | 2015-05-21 17:39:29 -0400 |
commit | 3205f8063b6cc54b20d5080fb79dfcbd9c39e93d (patch) | |
tree | 44b45b0f1fc50b7e3e5318d83d7e19390373745e /kernel/trace/ring_buffer.c | |
parent | d0ee8f4a1f5f3df933cdc9a80f5dea13e2fb5022 (diff) | |
download | linux-3205f8063b6cc54b20d5080fb79dfcbd9c39e93d.tar.bz2 |
ring-buffer: Add unlikelys to make fast path the default
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>
Diffstat (limited to 'kernel/trace/ring_buffer.c')
-rw-r--r-- | kernel/trace/ring_buffer.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index a4bdd63219be..043920c6d7c2 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2741,23 +2741,23 @@ 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); |