From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shan Wei Subject: [PATCH 0/9 v4] use efficient this_cpu_* helper Date: Tue, 13 Nov 2012 09:51:37 +0800 Message-ID: <50A1A7A9.6050501@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE To: cl@linux-foundation.org, David Miller , NetDev , Kernel-Maillist , Shan Wei Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org this_cpu_ptr/this_cpu_read is faster than per_cpu_ptr(p, smp_processor_= id())=20 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.= =20 this_cpu_ptr relocates and address. this_cpu_read() relocates the addre= ss and performs the fetch. If you want to operate on rda(defined as per_cp= u)=20 then you can only use this_cpu_ptr. this_cpu_read() saves you more inst= ructions since it can do the relocation and the fetch in one instruction. per_cpu_ptr(p, smp_processor_id())=EF=BC=9A 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 V4: 1. [read|write]ing fields of struct rds_ib_cache_head using __this_cpu_= * operation for rds subsystem. see patch2 2. fix bug in xfrm to read pointer. see patch3.=20 3. avoid type cast in patch7. 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.=20 Changelog V2: 1. Use this_cpu_read directly instead of ref to field of per-cpu variab= le. 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. =20 $ git diff --stat d4185bbf62a5d8d777ee445db1581beb17882a07 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.h | 2 +- net/rds/ib_recv.c | 24 +++++++++++++----------- net/xfrm/xfrm_ipcomp.c | 8 +++----- 12 files changed, 29 insertions(+), 38 deletions(-)