Messages in this thread | | | Date | Fri, 09 Nov 2012 10:20:06 +0800 | From | Shan Wei <> | Subject | [PATCH 0/9 v3] use efficient this_cpu_* helper |
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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. If you want to operate on rda(defined as per_cpu) then you can only use this_cpu_ptr. 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
Changelog V3: 1. use this_cpu_read directly read member of per-cpu variable, so that droping the this_cpu_ptr operation. 2. for preemption off and bottom halves off case, use __this_cpu_read instead of this_cpu_read.
Changelog V2: 1. Use this_cpu_read directly instead of ref to field of per-cpu variable. 2. Patch5 about ftrace is dropped from this series. 3. Add new patch9 to replace get_cpu;per_cpu_ptr;put_cpu with this_cpu_add opt. 4. For preemption disable case, use __this_cpu_read instead.
$ git diff --stat 7da716aee2532399e213a14f656d304098f67a11.. drivers/clocksource/arm_generic.c | 2 +- kernel/padata.c | 5 ++--- kernel/rcutree.c | 2 +- kernel/trace/blktrace.c | 2 +- kernel/trace/trace.c | 5 +---- net/batman-adv/main.h | 4 +--- net/core/flow.c | 4 +--- net/openvswitch/datapath.c | 4 ++-- net/openvswitch/vport.c | 5 ++--- net/rds/ib_recv.c | 2 +- net/xfrm/xfrm_ipcomp.c | 7 ++----- 11 files changed, 15 insertions(+), 27 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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