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Date: Fri, 29 Oct 2010 10:56:49 -0500 (CDT)
From: Christoph Lameter <cl@...ux.com>
To: akpm@...ux-foundation.org
cc: eric.dumazet@...il.com, linux-kernel@...r.kernel.org
Subject: percpucounter: Optimize __percpu_counter_add a bit through the use
of this_cpu operations
this_cpu_* operations can be used to optimize __percpu_counter_add a
bit. Avoids some address arithmetic and saves 12 bytes.
Before:
00000000000001d3 <__percpu_counter_add>:
1d3: 55 push %rbp
1d4: 48 89 e5 mov %rsp,%rbp
1d7: 41 55 push %r13
1d9: 41 54 push %r12
1db: 53 push %rbx
1dc: 48 89 fb mov %rdi,%rbx
1df: 48 83 ec 08 sub $0x8,%rsp
1e3: 4c 8b 67 30 mov 0x30(%rdi),%r12
1e7: 65 4c 03 24 25 00 00 add %gs:0x0,%r12
1ee: 00 00
1f0: 4d 63 2c 24 movslq (%r12),%r13
1f4: 48 63 c2 movslq %edx,%rax
1f7: 49 01 f5 add %rsi,%r13
1fa: 49 39 c5 cmp %rax,%r13
1fd: 7d 0a jge 209 <__percpu_counter_add+0x36>
1ff: f7 da neg %edx
201: 48 63 d2 movslq %edx,%rdx
204: 49 39 d5 cmp %rdx,%r13
207: 7f 1e jg 227 <__percpu_counter_add+0x54>
209: 48 89 df mov %rbx,%rdi
20c: e8 00 00 00 00 callq 211 <__percpu_counter_add+0x3e>
211: 4c 01 6b 18 add %r13,0x18(%rbx)
215: 48 89 df mov %rbx,%rdi
218: 41 c7 04 24 00 00 00 movl $0x0,(%r12)
21f: 00
220: e8 00 00 00 00 callq 225 <__percpu_counter_add+0x52>
225: eb 04 jmp 22b <__percpu_counter_add+0x58>
227: 45 89 2c 24 mov %r13d,(%r12)
22b: 5b pop %rbx
22c: 5b pop %rbx
22d: 41 5c pop %r12
22f: 41 5d pop %r13
231: c9 leaveq
232: c3 retq
After:
00000000000001d3 <__percpu_counter_add>:
1d3: 55 push %rbp
1d4: 48 63 ca movslq %edx,%rcx
1d7: 48 89 e5 mov %rsp,%rbp
1da: 41 54 push %r12
1dc: 53 push %rbx
1dd: 48 89 fb mov %rdi,%rbx
1e0: 48 8b 47 30 mov 0x30(%rdi),%rax
1e4: 65 44 8b 20 mov %gs:(%rax),%r12d
1e8: 4d 63 e4 movslq %r12d,%r12
1eb: 49 01 f4 add %rsi,%r12
1ee: 49 39 cc cmp %rcx,%r12
1f1: 7d 0a jge 1fd <__percpu_counter_add+0x2a>
1f3: f7 da neg %edx
1f5: 48 63 d2 movslq %edx,%rdx
1f8: 49 39 d4 cmp %rdx,%r12
1fb: 7f 21 jg 21e <__percpu_counter_add+0x4b>
1fd: 48 89 df mov %rbx,%rdi
200: e8 00 00 00 00 callq 205 <__percpu_counter_add+0x32>
205: 4c 01 63 18 add %r12,0x18(%rbx)
209: 48 8b 43 30 mov 0x30(%rbx),%rax
20d: 48 89 df mov %rbx,%rdi
210: 65 c7 00 00 00 00 00 movl $0x0,%gs:(%rax)
217: e8 00 00 00 00 callq 21c <__percpu_counter_add+0x49>
21c: eb 04 jmp 222 <__percpu_counter_add+0x4f>
21e: 65 44 89 20 mov %r12d,%gs:(%rax)
222: 5b pop %rbx
223: 41 5c pop %r12
225: c9 leaveq
226: c3 retq
Signed-off-by: Christoph Lameter <cl@...ux.com>
---
lib/percpu_counter.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
Index: linux-2.6/lib/percpu_counter.c
===================================================================
--- linux-2.6.orig/lib/percpu_counter.c 2010-10-29 10:45:06.000000000 -0500
+++ linux-2.6/lib/percpu_counter.c 2010-10-29 10:48:40.000000000 -0500
@@ -72,18 +72,16 @@ EXPORT_SYMBOL(percpu_counter_set);
void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
{
s64 count;
- s32 *pcount;
preempt_disable();
- pcount = this_cpu_ptr(fbc->counters);
- count = *pcount + amount;
+ count = this_cpu_read(*fbc->counters) + amount;
if (count >= batch || count <= -batch) {
spin_lock(&fbc->lock);
fbc->count += count;
- *pcount = 0;
+ this_cpu_write(*fbc->counters, 0);
spin_unlock(&fbc->lock);
} else {
- *pcount = count;
+ this_cpu_write(*fbc->counters, count);
}
preempt_enable();
}
--
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