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| author | Shan Wei <shanwei88@gmail.com> | 2012-11-13 20:36:00 +0800 |
|---|---|---|
| committer | Steffen Klassert <steffen.klassert@secunet.com> | 2012-11-13 14:38:52 +0100 |
| commit | f7c83bcbfaf5c848018680a499aa6b50b32f3085 (patch) | |
| tree | ad6bd047ef0d545c48637900a8e1d7e87bf38a06 /net | |
| parent | aafd0d88ee3a009b3f4f576a8e6e114d4810e489 (diff) | |
| download | linux-f7c83bcbfaf5c848018680a499aa6b50b32f3085.tar.bz2 | |
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')
| -rw-r--r-- | net/xfrm/xfrm_ipcomp.c | 8 |
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; } } |