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Message-ID: <0000013b047079ab-01971b64-07e2-4f2e-a204-6baff2180fc3-000000@email.amazonses.com>
Date: Thu, 15 Nov 2012 14:19:38 +0000
From: Christoph Lameter <cl@...ux.com>
To: Tejun Heo <htejun@...il.com>
cc: David Miller <davem@...emloft.net>,
NetDev <netdev@...r.kernel.org>, Shan Wei <shanwei88@...il.com>,
Kernel-Maillist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/9 v4] use efficient this_cpu_* helper
Tejon: Could you pick up this patchset?
On Tue, 13 Nov 2012, Shan Wei wrote:
> 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 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.
> 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.
>
> 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 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(-)
>
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