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authorShan Wei <shanwei88@gmail.com>2012-11-13 16:36:00 +0400
committerSteffen Klassert <steffen.klassert@secunet.com>2012-11-13 17:38:52 +0400
commitf7c83bcbfaf5c848018680a499aa6b50b32f3085 (patch)
treead6bd047ef0d545c48637900a8e1d7e87bf38a06 /net/xfrm
parentaafd0d88ee3a009b3f4f576a8e6e114d4810e489 (diff)
downloadlinux-f7c83bcbfaf5c848018680a499aa6b50b32f3085.tar.xz
net: xfrm: use __this_cpu_read per-cpu helper
this_cpu_ptr/this_cpu_read is faster than per_cpu_ptr(p, smp_processor_id()) and can reduce memory accesses. The latter helper needs to find the offset for current cpu, and needs more assembler instructions which objdump shows in following. this_cpu_ptr relocates and address. this_cpu_read() relocates the address and performs the fetch. this_cpu_read() saves you more instructions since it can do the relocation and the fetch in one instruction. per_cpu_ptr(p, smp_processor_id()): 1e: 65 8b 04 25 00 00 00 00 mov %gs:0x0,%eax 26: 48 98 cltq 28: 31 f6 xor %esi,%esi 2a: 48 c7 c7 00 00 00 00 mov $0x0,%rdi 31: 48 8b 04 c5 00 00 00 00 mov 0x0(,%rax,8),%rax 39: c7 44 10 04 14 00 00 00 movl $0x14,0x4(%rax,%rdx,1) this_cpu_ptr(p) 1e: 65 48 03 14 25 00 00 00 00 add %gs:0x0,%rdx 27: 31 f6 xor %esi,%esi 29: c7 42 04 14 00 00 00 movl $0x14,0x4(%rdx) 30: 48 c7 c7 00 00 00 00 mov $0x0,%rdi Signed-off-by: Shan Wei <davidshan@tencent.com> Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Diffstat (limited to 'net/xfrm')
-rw-r--r--net/xfrm/xfrm_ipcomp.c8
1 files changed, 3 insertions, 5 deletions
diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
index e5246fbe36c4..2906d520eea7 100644
--- a/net/xfrm/xfrm_ipcomp.c
+++ b/net/xfrm/xfrm_ipcomp.c
@@ -276,18 +276,16 @@ static struct crypto_comp * __percpu *ipcomp_alloc_tfms(const char *alg_name)
struct crypto_comp * __percpu *tfms;
int cpu;
- /* This can be any valid CPU ID so we don't need locking. */
- cpu = raw_smp_processor_id();
list_for_each_entry(pos, &ipcomp_tfms_list, list) {
struct crypto_comp *tfm;
- tfms = pos->tfms;
- tfm = *per_cpu_ptr(tfms, cpu);
+ /* This can be any valid CPU ID so we don't need locking. */
+ tfm = __this_cpu_read(*pos->tfms);
if (!strcmp(crypto_comp_name(tfm), alg_name)) {
pos->users++;
- return tfms;
+ return pos->tfms;
}
}