为什么OpenMP SIMD指令会降低性能? [英] Why the OpenMP SIMD directive reduces performance?
问题描述
我正在学习如何在OpenMP / Fortran中使用SIMD指令。我
写了简单的代码:
程序循环
隐式无
integer :: i ,j
real * 8 :: x
x = 0.0
do i = 1,10000
do j = 1,10000000
x = x + 1.0 /(1.0 * i)
enddo
enddo
print *,x
结束程序循环
当我编译这段代码并运行它时,我得到:
ifort -O3 -vec-report3 -xhost loop_simd.f90
loop_simd.f90(10):(col。12)备注:LOOP WAS VECTORIZED
loop_simd。 f90(9):(col。7)备注:循环未被矢量化:不是内循环
时间./a.out
97876060.8355515
真实0m8。 940s
用户0m8.937s
sys 0m0.005s
我做了什么编译器建议关于不是内部循环,
添加了一个SIMD崩溃(2)指令:
程序循环
隐式非e
integer :: i,j
real * 8 :: x
x = 0.0
!$ omp simd collapse(2)reduction(+ :x)
do i = 1,10000
do j = 1,10000000
x = x + 1.0 /(1.0 * i)
enddo
enddo
print *,x
结束程序循环
然后我再次编译并运行代码,并得到以下
输出:
ifort -O3 - vec-report3 -openmp -xhost loop_simd.f90
loop_simd.f90(8):(col。 7)备注:OpenMP SIMD LOOP WECT VECTORIZED
时间./a.out
97876054.9903757
真实0m26.535s
用户0m26.540s
sys 0m0.003s
我不知道为什么SIMD会降低性能?
当SIMD比标准的Fortran代码更好吗?
.section .text
.LNDBG_TX:
#mark_description英特尔(R)Fortran英特尔(R)64编译器XE,用于运行在英特尔(R)64,14.0.2.144版本2上的应用程序;
#mark_description0140120;
#mark_description-O3 -vec-report3 -openmp -xhost -S;
.fileloop_simd.f90
.text
..TXTST0:
L__routine_start_MAIN___0:
# - 开始MAIN__
#mark_begin;
.align 16,0x90
.globl MAIN__
MAIN__:
..B1.1:#Preds ..B1.0
..___ tag_value_MAIN __。1:# 1.9
..LN0:
.file 1loop_simd.f90
.loc 1 1 is_stmt 1
pushq%rbp#1.9
..___ tag_value_MAIN __。3: #
..LN1:
movq%rsp,%rbp#1.9
..___ tag_value_MAIN __。4:#
..LN2:
andq $ -128,% rsp#1.9
..LN3:
subq $ 128,%rsp#1.9
..LN4:
movq $ 0x0000117fe,%rsi#1.9
..LN5:
movl $ 3,%edi#1.9
..LN6:
call __intel_new_feature_proc_init#1.9
..LN7:
#LOE rbx r12 r13 r14 r15
..B1.12:#Preds ..B1.1
..LN8:
vstmxcsr( %rsp)#1.9
..LN9:
movl $ .2.3_2_kmpc_loc_struct_pack.1,%edi#1.9
..LN10:
xorl%esi,%esi#1.9
..LN11:
orl $ 32832,(%rsp)#1.9
..LN12:
xorl%eax,%eax#1.9
..LN13:
vldmxcsr(%rsp)#1.9
..___ tag_value_MAIN __。6:#1.9
..LN14:
call __kmpc_begin#1.9
..___ tag_value_MAIN __。7:#
..LN15:
#LOE rbx r12 r13 r14 r15
..B1.2:#Preds ..B1.12
..LN16:
movl $ __ NLITPACK_0.0.1,%edi#1.9
..LN17:
call for_set_reentrancy#1.9
..LN18 :
#LOE rbx r12 r13 r14 r15
..B1.3:#Preds ..B1.2
..LN19:
.loc 1 8 is_stmt 1
movl $ 4,%eax#8.7
..LN20:
.loc 1 6 is_stmt 1
vxorpd%ymm2,%ymm2,%ymm2#6.7
..LN21:
.loc 1 8 is_stmt 1
vmovd%eax,%xmm0#8.7
..LN22:
xorl%eax,%eax#8.7
..LN23:
vpshufd $ 0,%xmm0,%xmm1#8.7
..LN24:
vmovdqu .L_2il0floatpacket.19(%rip),%xmm0#8.7
..LN25:
#LOE rbx r12 r13 r14 r15 eax xmm0 xmm1 ymm2
..B1.4:#Preds ..B1.6 ..B1.3
..LN26:
.loc 1 11 is_stmt 1
vcvtdq2ps %xmm0,%xmm3#11.34
..LN27:
vrcpps%xmm3,%xmm5#11.28
..LN28:
vmulps%xmm3,%xmm5,%xmm4#11.28
..LN29:
vaddps%xmm5,%xmm5,%xmm6#11.28
..LN30:
vmulps%xmm5,%xmm4,%xmm7#11.28
..LN31:
.loc 1 10 is_stmt 1
xorl%edx,%edx#10.12
..LN32:
.loc 1 11 is_stmt 1
vsubps% xmm7,%xmm6,%xmm8#11.28
..LN33:
vcvtps2pd%xmm8,%ymm3#11.28
..LN34:
#LOE rbx r12 r13 r14 r15 eax edx xmm0 xmm1 ymm2 ymm3
..B1.5:#Preds ..B1.5 ..B1.4
..LN35:
.loc 1 10 is_stmt 1
incl%edx#10.12
..LN36:
.loc 1 11 is_stmt 1
vaddpd%ymm3,%ymm2,%ymm2#11.17
..LN37:
.loc 1 10 is_stmt 1
cmpl $ 10000000,%edx#10.12
..LN38:
jb ..B1.5#Prob 99%#10.12
..LN39:
#LOE rbx r12 r13 r14 r15 eax edx xmm0 xmm1 ymm2 ymm3
..B1.6:#Preds ..B1.5
..LN40:
.loc 1 8 is_stmt 1
addl $ 4, %eax#8.7
..LN41:
.loc 1 10 is_stmt 1
vpaddd%xmm1,%xmm0,%xmm0#10.12
..LN42:
。 loc 1 8 is_stmt 1
cmpl $ 10000,%eax #8.7
..LN43:
jb ..B1.4#问题66%#8.7
..LN44:
#LOE rbx r12 r13 r14 r15 eax xmm0 xmm1 ymm2
..B1.7:#Preds ..B1.6
..LN45:
.loc 1 6 is_stmt 1
..LN46:
.loc 1 15 is_stmt 1
lea(%rsp),%rdi#15.7
..LN47:
.loc 1 6 is_stmt 1
vextractf128 $ 1,%ymm2,%xmm0#6.7
..LN48:
.loc 1 15 is_stmt 1
movl $ -1,%esi#15.7
..LN49:
.loc 1 6 is_stmt 1
vaddpd%xmm0,%xmm2,%xmm1#6.7
..LN50:
vunpckhpd%xmm1,%xmm1,%xmm3#6.7
..LN51:
.loc 1 15 is_stmt 1
lea 64(%rsp),%r8#15.7
..LN52:
movq $ 0x1208384ff00,%rdx#15.7
..LN53:
movl $ __ STRLITPACK_0.0.1,%ecx#15.7
..LN54:
xorl%eax,%eax#15.7
..LN55:
.loc 1 6 is_stmt 1
vaddsd%xmm3,%xmm1,%xmm4#6.7
..LN56:
.loc 1 15 is_stmt 1
vmovsd%xmm4,64(%rsp)#15.7
..LN57:
movq $ 0,(%rsp)#15.7
。 .LN58:
vzeroupper#15.7
..LN59:
call for_write_seq_lis#15.7
..LN60:
#LOE rbx r12 r13 r14 r15
。 .B1.8:#Preds ..B1.7
..LN61:
.loc 1 18 is_stmt 1
movl $ .2.3_2_kmpc_loc_struct_pack.12,%edi #18.1
..LN62:
xorl%eax,%eax#18.1
..___ tag_value_MAIN __。8:#18.1
..LN63:
call __kmpc_end#18.1
..___ tag_value_MAIN __。9:#
..LN64:
#LOE rbx r12 r13 r14 r15
..B1.9:#Preds ..B1.8
..LN65:
movl $ 1,%eax#18.1
..LN66:
movq%rbp,%rsp#18.1
..LN67:
popq% rbp#18.1
..___ tag_value_MAIN __。10:#
..LN68:
ret#18.1
.align 16,0x90
..___ tag_value_MAIN __。12:#
..LN69:
#LOE
..LN70:
#mark_end;
.type MAIN __,@ function
.size MAIN __,.- MAIN__
..LNMAIN __。71:
.LNMAIN__:
.data
.align 4
.align 4
.2.3_2_kmpc_loc_struct_pack.1:
.long 0
.long 2
.long 0
.long 0
.quad.2.3_2__kmpc_loc_pack.0
.align 4
.2.3_2__kmpc_loc_pack.0:
.byte 59
.byte 117
.byte 110
。字节107
.byte 110
.byte 111
.byte 119
.byte 110
.byte 59
.byte 77
.byte 65
.byte 73
.byte 78
.byte 95
.byte 95
.byte 59
.byte 49
.byte 59
.byte 49
.byte 59
.byte 59
.space 3,0x00#pad
.align 4
.2.3_2_kmpc_loc_struct_pack.12:
.long 0
.long 2
.long 0
.long 0
.quad .2.3_2__kmpc_loc_pack.11
.alig n 4
.2.3_2__kmpc_loc_pack.11:
.byte 59
.byte 117
.byte 110
.byte 107
.byte 110
。字节111
.byte 119
.byte 110
.byte 59
.byte 77
.byte 65
.byte 73
.byte 78
.byte 95
.byte 95
.byte 59
.byte 49
.byte 56
.byte 59
。字节49
.byte 56
.byte 59
.byte 59
.section .rodata,a
.align 16
.align 8
__NLITPACK_0.0.1:
.long 0x00000002,0x00000000
.align 4
__STRLITPACK_0.0.1:
.byte 48
.byte 1
。字节1
.byte 0
.byte 0
.data
# - 结束MAIN__
.section .rodata,a
.space 3 ,0x00#pad
.align 16
.L_2il0floatpacket.19:
.long 0x00000001,0x00000002,0x00000003,0x00000004
.type .L2i l0floatpacket.19,@ object
.size .L_2il0floatpacket.19,16
.align 16
.L_2il0floatpacket.20:
.long 0x3f800000,0x3f800000,0x3f800000,0x3f800000
.type .L_2il0floatpacket.20,@ object
.size .L_2il0floatpacket.20,16
.data
.section .note.GNU-stack,
#End
非openmp代码的ASM输出
<$英特尔(R)Fortran英特尔(R)64编译器XE适用于在英特尔(R)64上运行的应用程序,版本14.0.2.144 Build 2;
#mark_description0140120;
#mark_description-O3 -vec-report3 -xhost -S;
.fileloop_simd.f90
.text
..TXTST0:
L__routine_start_MAIN___0:
# - 开始MAIN__
#mark_begin;
.align 16,0x90
.globl MAIN__
MAIN__:
..B1.1:#Preds ..B1.0
..___ tag_value_MAIN __。1:# 1.9
..LN0:
.file 1loop_simd.f90
.loc 1 1 is_stmt 1
pushq%rbp#1.9
..___ tag_value_MAIN __。3: #
..LN1:
movq%rsp,%rbp#1.9
..___ tag_value_MAIN __。4:#
..LN2:
andq $ -128,% rsp#1.9
..LN3:
subq $ 128,%rsp#1.9
..LN4:
movq $ 0x0000117fe,%rsi#1.9
..LN5:
movl $ 3,%edi#1.9
..LN6:
call __intel_new_feature_proc_init#1.9
..LN7:
#LOE rbx r12 r13 r14 r15
..B1.10:#Preds ..B1.1
..LN8:
vstmxcsr( %rsp)#1.9
..LN9:
movl $ __ NLITPACK_0.0.1,%edi#1.9
..LN10:
orl $ 32832,(%rsp)#1.9
..LN11:
vldmxcsr(%rsp)#1.9
..LN12:
call for_set_reentrancy#1.9
..LN13:
#LOE rbx r12 r13 r14 r15
..B1.2:#Preds ..B1.10
..LN14:
.loc 1 6 is_stmt 1
..LN15:
。 loc 1 11 is_stmt 1
vmovss .L_2il0floatpacket.0(%rip),%xmm6#11.28
..LN16:
.loc 1 9 is_stmt 1
xorl%eax,% eax#9.7
..LN17:
.lo c 1 6 is_stmt 1
vxorpd%ymm8,%ymm8,%ymm8#6.7
..LN18:
vmovapd%ymm8,%ymm7#6.7
..LN19:
vmovapd%ymm8,%ymm0#6.7
..LN20:
vmovapd%ymm8,%ymm1#6.7
..LN21:
vmovapd%ymm8,%ymm2#6.7
..LN22:
vmovapd%ymm8,%ymm3#6.7
..LN23:
vmovapd%ymm8,%ymm4#6.7
..LN24:
vmovapd%ymm8,%ymm5#6.7
..LN25:
#LOE rbx r12 r13 r14 r15 eax xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8
..B1.3:# Preds ..B1.5 ..B1.2
..LN26:
incl%eax#
..LN27:
.loc 1 11 is_stmt 1
vxorps%xmm9,%xmm9,%xmm9#11.28
..LN28:
vcvtsi2ss%eax,%xmm9,%xmm9#11.28
..LN29:
vdivss%xmm9,%xmm6,%xmm10#11.28
..LN30:
vcvtss2sd%xmm10,%xmm10,%xmm10#11.28
..LN31:
vmovddup%xmm10,%xmm11#11.28
..LN32:
.loc 1 10 is_stmt 1
xorl%edx,%edx#10.12
..LN33:
.loc 1 11 is_stmt 1
vinsertf128 $ 1,%xmm11,%ymm11,%ymm9#11.28
..LN34:
#LOE rbx r12 r13 r14 r15 eax edx xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8 ymm9
..B1.4:#Preds ..B1.4 ..B1.3
..LN35:
.loc 1 10 is_stmt 1
addl $ 32 ,%edx #10.12
..LN36:
.loc 1 11 is_stmt 1
vaddpd%ymm9,%ymm8,%ymm8#11.17
..LN37:
vaddpd%ymm7 ,%ymm9,%ymm7#11.17
..LN38:
vaddpd%ymm0,%ymm9,%ymm0#11.17
..LN39:
vaddpd%ymm1,%ymm9, %ymm1#11.17
..LN40:
vaddpd%ymm2,%ymm9,%ymm2#11.17
..LN41:
vaddpd%ymm3,%ymm9,%ymm3#11.17
..LN42:
vaddpd%ymm4,%ymm9,%ymm4#11.17
..LN43:
vaddpd%ymm5,%ymm9,%ymm5#11.17
..LN44:
.loc 1 10 is_stmt 1
cmpl $ 10000000,%edx#10.12
..LN45:
jb ..B1.4#Prob 99%#10.12
..LN46:
#LOE rbx r12 r13 r14 r15 eax edx xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8 ymm9
..B1.5:#Preds ..B1.4
..LN47:
.loc 1 9 is_stmt 1
cmpl $ 10000,%eax#9.7
..LN48:
jb ..B1.3#问题66%#9.7
..LN49:
#LOE rbx r12 r13 r14 r15 eax xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8
..B1.6:#Preds ..B1.5
..LN50:
.loc 1 6 is_stmt 1
vaddpd%ymm7,%ymm8,%ymm6#6.7
..LN51:
.loc 1 15 is_stmt 1
lea(%rsp),%rdi#15.7
..LN52:
.loc 1 6 is_stmt 1
vaddpd%ymm1,%ymm0,%ymm0#6.7
..LN53:
vaddpd%ymm3,% ymm2,%ymm1#6.7
..LN54:
vaddpd%ymm5,%ymm4,%ymm2#6.7
..LN55:
vaddpd%ymm0,%ymm6,%ymm3#6.7
..LN56:
vaddpd%ymm2, %ymm1,%ymm4#6.7
..LN57:
vaddpd%ymm4,%ymm3,%ymm5#6.7
..LN58:
.loc 1 15 is_stmt 1
movl $ -1,%esi#15.7
..LN59:
movq $ 0x1208384ff00,%rdx#15.7
..LN60:
movl $ __ STRLITPACK_0.0.1,% ecx#15.7
..LN61:
xorl%eax,%eax#15.7
..LN62:
lea 64(%rsp),%r8#15.7
..LN63:
movq $ 0,(%rsp)#15.7
..LN64:
.loc 1 6 is_stmt 1
vextractf128 $ 1,%ymm5,%xmm7 #6.7
..LN65:
vaddpd%xmm7,%xmm5,%xmm8#6.7
..LN66:
vunpckhpd%xmm8,%xmm8,%xmm9#6.7
..LN67:
vaddsd%xmm9,%xmm8,%xmm10#6.7
..LN68:
.loc 1 15 is_stmt 1
vmovsd%xmm10,64(% rsb)#15.7
..LN69:
vzeroupper#15.7
..LN70:
call for_write_seq_lis#15.7
..LN71:
#LOE rbx r12 r13 r14 r15
..B1.7:#Preds ..B1.6
..LN72:
.loc 1 18 is_stmt 1
movl $ 1,%eax#18.1
..LN73:
movq%rbp,%rsp#18.1
..LN74:
popq%rbp#18.1
..__ _tag_value_MAIN __。6:#
..LN75:
ret#18.1
.align 16,0x90
..___ tag_value_MAIN __。8:#
..LN76:
#LOE
..LN77:
#mark_end;
.type MAIN __,@ function
.size MAIN __,.- MAIN__
..LNMAIN __。78:
.LNMAIN__:
.section .rodata,a
.align 8
.align 8
__NLITPACK_0.0.1:
.long 0x00000000,0x00000000
.align 4
__STRLITPACK_0.0.1:
.byte 48
.byte 1
.byte 1
.byte 0
.byte 0
.data
# - End MAIN__
.section .rodata,a
.space 3,0x00#pad
.align 4
.L_2il0floatpacket.0:
.long 0x3f800000 $ b $ .type .L_2il0floatpacket .0,@ object
.size .L_2il0floatpacket.0,4
.data
.section .note.GNU-stack,
#End
解决方案 借助OpenMP ,Ifort使用SIMD矢量化外循环(超过 i
),所以基本上所有的时间都花在做
pre $ ##使用1.0 /(1.0 * i),
#和j =%edx = 0的4个副本设置ymm3
..B1.5:do {
incl%edx#j ++
vaddpd%ymm3,%ymm2,%ymm2#ymm3 + ymm2 => ymm2
cmpl $ 10000000,%edx} while(j <10000000);
jb ..B1.5#Prob 99%
<$ c $的10M迭代c> vaddpd
将完全支配循环外部的所有成本,所以重要的是这个内部循环执行10k / 4次。 (注意加$ 4,%eax
/ cmp $ 10000,%eax
/ jb
,分支目标返回到内部循环之前。)由于它只使用一个累加器,所以吞吐量受到循环运行依赖(3个周期)。
没有OpenMP:
仍然在做全部工作,而不是优化掉任何循环。
它像 #pragma openmp $ c一样进行自动矢量化$ c>,但使用多个累加器来提高并行性。多个添加指令可以一次在飞行中,而不是每个都依赖于前一个。
内部循环的设置非常相似,然后内部循环循环是:
##使用1.0 /(1.0 * i),
4副本设置ymm3。 B1.4:
addl $ 32,%edx#10.12
vaddpd%ymm9,%ymm8,%ymm8#ymm8 + ymm9 => ymm8
vaddpd%ymm7,%ymm9,%ymm7#ymm7 + ymm9 => ymm7
vaddpd%ymm0,%ymm9,%ymm0#ymm0 + ymm9 => ymm0
vaddpd%ymm1,%ymm9,%ymm1#...
vaddpd%ymm2,%ymm9,%ymm2
vaddpd%ymm3,%ymm9,%ymm3
vaddpd% ymm4,%ymm9,%ymm4
vaddpd%ymm5,%ymm9,%ymm5
cmpl $ 10000000,%edx
jb ..B1.4#问题99%
#然后将8个矢量累加器合并到一个,然后水平和。
8个累加器可以保留8 这完美地解释了3倍速比:26.535 / 8.940 = 2.97〜= 3 。 ( I am learning how to use SIMD directives with OpenMP/Fortran. I
wrote the simple code: when I compile this code and run it I get: I did what the compiler suggested about the "not inner loop" and
added a SIMD collapse(2) directive: then I compiled and run the code again and I got the following
output: What I don't know is why the performance decreases with SIMD?
And when SIMD will be better than standard Fortran code? ASM output for the non-openmp code
With OpenMP, Ifort is using SIMD to vectorize the outer loop (over 10M iterations of Since it's only using a single accumulator, throughput is limited by the loop-carried dependency (3 cycles). It's still doing the full amount of work, not optimizing away any of the loops. It auto-vectorizes like with The setup for the inner loop is very similar, and then the inner loop is: 8 accumulators could keep 8 This perfectly explains the 3x speed ratio: 26.535 / 8.940 = 2.97 ~= 3. ( Unrolling with this many accumulators will help for Skylake, where FP add has 4 cycle latency and two per cycle throughput. (SKL dropped the lower-latency dedicated vector FP add unit from port 1, and runs it in the improved 4c-latency FMA units on ports 0 and 1.) 这篇关于为什么OpenMP SIMD指令会降低性能?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋! vaddpd
s in立即飞行,但Intel SnB / IvB的延迟仅为3个周期(请参阅 Agner Fog's insn表格)。你没有说你使用的是什么微架构,但是我可以从 -xhost
使用AVX1而不是AVX2的事实推断Sandybridge / Ivybridge。 (以 vmovddup
/ vinsertf128
广播,而不是AVX2 vbroadcastsd%xmm9,%ymm9 < code $)
vaddpd
)在Skylake Intel CPU之前的每个时钟上的吞吐量为1,延迟= 3。由于指令级增加,此版本受吞吐量而非延迟的限制并行性)。
program loop
implicit none
integer :: i,j
real*8 :: x
x = 0.0
do i=1,10000
do j=1,10000000
x = x + 1.0/(1.0*i)
enddo
enddo
print*, x
end program loop
ifort -O3 -vec-report3 -xhost loop_simd.f90
loop_simd.f90(10): (col. 12) remark: LOOP WAS VECTORIZED
loop_simd.f90(9): (col. 7) remark: loop was not vectorized: not inner loop
time ./a.out
97876060.8355515
real 0m8.940s
user 0m8.937s
sys 0m0.005s
program loop
implicit none
integer :: i,j
real*8 :: x
x = 0.0
!$omp simd collapse(2) reduction(+:x)
do i=1,10000
do j=1,10000000
x = x + 1.0/(1.0*i)
enddo
enddo
print*, x
end program loop
ifort -O3 -vec-report3 -openmp -xhost loop_simd.f90
loop_simd.f90(8): (col. 7) remark: OpenMP SIMD LOOP WAS VECTORIZED
time ./a.out
97876054.9903757
real 0m26.535s
user 0m26.540s
sys 0m0.003s
.section .text
.LNDBG_TX:
# mark_description "Intel(R) Fortran Intel(R) 64 Compiler XE for applications running on Intel(R) 64, Version 14.0.2.144 Build 2";
# mark_description "0140120";
# mark_description "-O3 -vec-report3 -openmp -xhost -S";
.file "loop_simd.f90"
.text
..TXTST0:
L__routine_start_MAIN___0:
# -- Begin MAIN__
# mark_begin;
.align 16,0x90
.globl MAIN__
MAIN__:
..B1.1: # Preds ..B1.0
..___tag_value_MAIN__.1: #1.9
..LN0:
.file 1 "loop_simd.f90"
.loc 1 1 is_stmt 1
pushq %rbp #1.9
..___tag_value_MAIN__.3: #
..LN1:
movq %rsp, %rbp #1.9
..___tag_value_MAIN__.4: #
..LN2:
andq $-128, %rsp #1.9
..LN3:
subq $128, %rsp #1.9
..LN4:
movq $0x0000117fe, %rsi #1.9
..LN5:
movl $3, %edi #1.9
..LN6:
call __intel_new_feature_proc_init #1.9
..LN7:
# LOE rbx r12 r13 r14 r15
..B1.12: # Preds ..B1.1
..LN8:
vstmxcsr (%rsp) #1.9
..LN9:
movl $.2.3_2_kmpc_loc_struct_pack.1, %edi #1.9
..LN10:
xorl %esi, %esi #1.9
..LN11:
orl $32832, (%rsp) #1.9
..LN12:
xorl %eax, %eax #1.9
..LN13:
vldmxcsr (%rsp) #1.9
..___tag_value_MAIN__.6: #1.9
..LN14:
call __kmpc_begin #1.9
..___tag_value_MAIN__.7: #
..LN15:
# LOE rbx r12 r13 r14 r15
..B1.2: # Preds ..B1.12
..LN16:
movl $__NLITPACK_0.0.1, %edi #1.9
..LN17:
call for_set_reentrancy #1.9
..LN18:
# LOE rbx r12 r13 r14 r15
..B1.3: # Preds ..B1.2
..LN19:
.loc 1 8 is_stmt 1
movl $4, %eax #8.7
..LN20:
.loc 1 6 is_stmt 1
vxorpd %ymm2, %ymm2, %ymm2 #6.7
..LN21:
.loc 1 8 is_stmt 1
vmovd %eax, %xmm0 #8.7
..LN22:
xorl %eax, %eax #8.7
..LN23:
vpshufd $0, %xmm0, %xmm1 #8.7
..LN24:
vmovdqu .L_2il0floatpacket.19(%rip), %xmm0 #8.7
..LN25:
# LOE rbx r12 r13 r14 r15 eax xmm0 xmm1 ymm2
..B1.4: # Preds ..B1.6 ..B1.3
..LN26:
.loc 1 11 is_stmt 1
vcvtdq2ps %xmm0, %xmm3 #11.34
..LN27:
vrcpps %xmm3, %xmm5 #11.28
..LN28:
vmulps %xmm3, %xmm5, %xmm4 #11.28
..LN29:
vaddps %xmm5, %xmm5, %xmm6 #11.28
..LN30:
vmulps %xmm5, %xmm4, %xmm7 #11.28
..LN31:
.loc 1 10 is_stmt 1
xorl %edx, %edx #10.12
..LN32:
.loc 1 11 is_stmt 1
vsubps %xmm7, %xmm6, %xmm8 #11.28
..LN33:
vcvtps2pd %xmm8, %ymm3 #11.28
..LN34:
# LOE rbx r12 r13 r14 r15 eax edx xmm0 xmm1 ymm2 ymm3
..B1.5: # Preds ..B1.5 ..B1.4
..LN35:
.loc 1 10 is_stmt 1
incl %edx #10.12
..LN36:
.loc 1 11 is_stmt 1
vaddpd %ymm3, %ymm2, %ymm2 #11.17
..LN37:
.loc 1 10 is_stmt 1
cmpl $10000000, %edx #10.12
..LN38:
jb ..B1.5 # Prob 99% #10.12
..LN39:
# LOE rbx r12 r13 r14 r15 eax edx xmm0 xmm1 ymm2 ymm3
..B1.6: # Preds ..B1.5
..LN40:
.loc 1 8 is_stmt 1
addl $4, %eax #8.7
..LN41:
.loc 1 10 is_stmt 1
vpaddd %xmm1, %xmm0, %xmm0 #10.12
..LN42:
.loc 1 8 is_stmt 1
cmpl $10000, %eax #8.7
..LN43:
jb ..B1.4 # Prob 66% #8.7
..LN44:
# LOE rbx r12 r13 r14 r15 eax xmm0 xmm1 ymm2
..B1.7: # Preds ..B1.6
..LN45:
.loc 1 6 is_stmt 1
..LN46:
.loc 1 15 is_stmt 1
lea (%rsp), %rdi #15.7
..LN47:
.loc 1 6 is_stmt 1
vextractf128 $1, %ymm2, %xmm0 #6.7
..LN48:
.loc 1 15 is_stmt 1
movl $-1, %esi #15.7
..LN49:
.loc 1 6 is_stmt 1
vaddpd %xmm0, %xmm2, %xmm1 #6.7
..LN50:
vunpckhpd %xmm1, %xmm1, %xmm3 #6.7
..LN51:
.loc 1 15 is_stmt 1
lea 64(%rsp), %r8 #15.7
..LN52:
movq $0x1208384ff00, %rdx #15.7
..LN53:
movl $__STRLITPACK_0.0.1, %ecx #15.7
..LN54:
xorl %eax, %eax #15.7
..LN55:
.loc 1 6 is_stmt 1
vaddsd %xmm3, %xmm1, %xmm4 #6.7
..LN56:
.loc 1 15 is_stmt 1
vmovsd %xmm4, 64(%rsp) #15.7
..LN57:
movq $0, (%rsp) #15.7
..LN58:
vzeroupper #15.7
..LN59:
call for_write_seq_lis #15.7
..LN60:
# LOE rbx r12 r13 r14 r15
..B1.8: # Preds ..B1.7
..LN61:
.loc 1 18 is_stmt 1
movl $.2.3_2_kmpc_loc_struct_pack.12, %edi #18.1
..LN62:
xorl %eax, %eax #18.1
..___tag_value_MAIN__.8: #18.1
..LN63:
call __kmpc_end #18.1
..___tag_value_MAIN__.9: #
..LN64:
# LOE rbx r12 r13 r14 r15
..B1.9: # Preds ..B1.8
..LN65:
movl $1, %eax #18.1
..LN66:
movq %rbp, %rsp #18.1
..LN67:
popq %rbp #18.1
..___tag_value_MAIN__.10: #
..LN68:
ret #18.1
.align 16,0x90
..___tag_value_MAIN__.12: #
..LN69:
# LOE
..LN70:
# mark_end;
.type MAIN__,@function
.size MAIN__,.-MAIN__
..LNMAIN__.71:
.LNMAIN__:
.data
.align 4
.align 4
.2.3_2_kmpc_loc_struct_pack.1:
.long 0
.long 2
.long 0
.long 0
.quad .2.3_2__kmpc_loc_pack.0
.align 4
.2.3_2__kmpc_loc_pack.0:
.byte 59
.byte 117
.byte 110
.byte 107
.byte 110
.byte 111
.byte 119
.byte 110
.byte 59
.byte 77
.byte 65
.byte 73
.byte 78
.byte 95
.byte 95
.byte 59
.byte 49
.byte 59
.byte 49
.byte 59
.byte 59
.space 3, 0x00 # pad
.align 4
.2.3_2_kmpc_loc_struct_pack.12:
.long 0
.long 2
.long 0
.long 0
.quad .2.3_2__kmpc_loc_pack.11
.align 4
.2.3_2__kmpc_loc_pack.11:
.byte 59
.byte 117
.byte 110
.byte 107
.byte 110
.byte 111
.byte 119
.byte 110
.byte 59
.byte 77
.byte 65
.byte 73
.byte 78
.byte 95
.byte 95
.byte 59
.byte 49
.byte 56
.byte 59
.byte 49
.byte 56
.byte 59
.byte 59
.section .rodata, "a"
.align 16
.align 8
__NLITPACK_0.0.1:
.long 0x00000002,0x00000000
.align 4
__STRLITPACK_0.0.1:
.byte 48
.byte 1
.byte 1
.byte 0
.byte 0
.data
# -- End MAIN__
.section .rodata, "a"
.space 3, 0x00 # pad
.align 16
.L_2il0floatpacket.19:
.long 0x00000001,0x00000002,0x00000003,0x00000004
.type .L_2il0floatpacket.19,@object
.size .L_2il0floatpacket.19,16
.align 16
.L_2il0floatpacket.20:
.long 0x3f800000,0x3f800000,0x3f800000,0x3f800000
.type .L_2il0floatpacket.20,@object
.size .L_2il0floatpacket.20,16
.data
.section .note.GNU-stack, ""
# End
.section .text
.LNDBG_TX:
# mark_description "Intel(R) Fortran Intel(R) 64 Compiler XE for applications running on Intel(R) 64, Version 14.0.2.144 Build 2";
# mark_description "0140120";
# mark_description "-O3 -vec-report3 -xhost -S";
.file "loop_simd.f90"
.text
..TXTST0:
L__routine_start_MAIN___0:
# -- Begin MAIN__
# mark_begin;
.align 16,0x90
.globl MAIN__
MAIN__:
..B1.1: # Preds ..B1.0
..___tag_value_MAIN__.1: #1.9
..LN0:
.file 1 "loop_simd.f90"
.loc 1 1 is_stmt 1
pushq %rbp #1.9
..___tag_value_MAIN__.3: #
..LN1:
movq %rsp, %rbp #1.9
..___tag_value_MAIN__.4: #
..LN2:
andq $-128, %rsp #1.9
..LN3:
subq $128, %rsp #1.9
..LN4:
movq $0x0000117fe, %rsi #1.9
..LN5:
movl $3, %edi #1.9
..LN6:
call __intel_new_feature_proc_init #1.9
..LN7:
# LOE rbx r12 r13 r14 r15
..B1.10: # Preds ..B1.1
..LN8:
vstmxcsr (%rsp) #1.9
..LN9:
movl $__NLITPACK_0.0.1, %edi #1.9
..LN10:
orl $32832, (%rsp) #1.9
..LN11:
vldmxcsr (%rsp) #1.9
..LN12:
call for_set_reentrancy #1.9
..LN13:
# LOE rbx r12 r13 r14 r15
..B1.2: # Preds ..B1.10
..LN14:
.loc 1 6 is_stmt 1
..LN15:
.loc 1 11 is_stmt 1
vmovss .L_2il0floatpacket.0(%rip), %xmm6 #11.28
..LN16:
.loc 1 9 is_stmt 1
xorl %eax, %eax #9.7
..LN17:
.loc 1 6 is_stmt 1
vxorpd %ymm8, %ymm8, %ymm8 #6.7
..LN18:
vmovapd %ymm8, %ymm7 #6.7
..LN19:
vmovapd %ymm8, %ymm0 #6.7
..LN20:
vmovapd %ymm8, %ymm1 #6.7
..LN21:
vmovapd %ymm8, %ymm2 #6.7
..LN22:
vmovapd %ymm8, %ymm3 #6.7
..LN23:
vmovapd %ymm8, %ymm4 #6.7
..LN24:
vmovapd %ymm8, %ymm5 #6.7
..LN25:
# LOE rbx r12 r13 r14 r15 eax xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8
..B1.3: # Preds ..B1.5 ..B1.2
..LN26:
incl %eax #
..LN27:
.loc 1 11 is_stmt 1
vxorps %xmm9, %xmm9, %xmm9 #11.28
..LN28:
vcvtsi2ss %eax, %xmm9, %xmm9 #11.28
..LN29:
vdivss %xmm9, %xmm6, %xmm10 #11.28
..LN30:
vcvtss2sd %xmm10, %xmm10, %xmm10 #11.28
..LN31:
vmovddup %xmm10, %xmm11 #11.28
..LN32:
.loc 1 10 is_stmt 1
xorl %edx, %edx #10.12
..LN33:
.loc 1 11 is_stmt 1
vinsertf128 $1, %xmm11, %ymm11, %ymm9 #11.28
..LN34:
# LOE rbx r12 r13 r14 r15 eax edx xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8 ymm9
..B1.4: # Preds ..B1.4 ..B1.3
..LN35:
.loc 1 10 is_stmt 1
addl $32, %edx #10.12
..LN36:
.loc 1 11 is_stmt 1
vaddpd %ymm9, %ymm8, %ymm8 #11.17
..LN37:
vaddpd %ymm7, %ymm9, %ymm7 #11.17
..LN38:
vaddpd %ymm0, %ymm9, %ymm0 #11.17
..LN39:
vaddpd %ymm1, %ymm9, %ymm1 #11.17
..LN40:
vaddpd %ymm2, %ymm9, %ymm2 #11.17
..LN41:
vaddpd %ymm3, %ymm9, %ymm3 #11.17
..LN42:
vaddpd %ymm4, %ymm9, %ymm4 #11.17
..LN43:
vaddpd %ymm5, %ymm9, %ymm5 #11.17
..LN44:
.loc 1 10 is_stmt 1
cmpl $10000000, %edx #10.12
..LN45:
jb ..B1.4 # Prob 99% #10.12
..LN46:
# LOE rbx r12 r13 r14 r15 eax edx xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8 ymm9
..B1.5: # Preds ..B1.4
..LN47:
.loc 1 9 is_stmt 1
cmpl $10000, %eax #9.7
..LN48:
jb ..B1.3 # Prob 66% #9.7
..LN49:
# LOE rbx r12 r13 r14 r15 eax xmm6 ymm0 ymm1 ymm2 ymm3 ymm4 ymm5 ymm7 ymm8
..B1.6: # Preds ..B1.5
..LN50:
.loc 1 6 is_stmt 1
vaddpd %ymm7, %ymm8, %ymm6 #6.7
..LN51:
.loc 1 15 is_stmt 1
lea (%rsp), %rdi #15.7
..LN52:
.loc 1 6 is_stmt 1
vaddpd %ymm1, %ymm0, %ymm0 #6.7
..LN53:
vaddpd %ymm3, %ymm2, %ymm1 #6.7
..LN54:
vaddpd %ymm5, %ymm4, %ymm2 #6.7
..LN55:
vaddpd %ymm0, %ymm6, %ymm3 #6.7
..LN56:
vaddpd %ymm2, %ymm1, %ymm4 #6.7
..LN57:
vaddpd %ymm4, %ymm3, %ymm5 #6.7
..LN58:
.loc 1 15 is_stmt 1
movl $-1, %esi #15.7
..LN59:
movq $0x1208384ff00, %rdx #15.7
..LN60:
movl $__STRLITPACK_0.0.1, %ecx #15.7
..LN61:
xorl %eax, %eax #15.7
..LN62:
lea 64(%rsp), %r8 #15.7
..LN63:
movq $0, (%rsp) #15.7
..LN64:
.loc 1 6 is_stmt 1
vextractf128 $1, %ymm5, %xmm7 #6.7
..LN65:
vaddpd %xmm7, %xmm5, %xmm8 #6.7
..LN66:
vunpckhpd %xmm8, %xmm8, %xmm9 #6.7
..LN67:
vaddsd %xmm9, %xmm8, %xmm10 #6.7
..LN68:
.loc 1 15 is_stmt 1
vmovsd %xmm10, 64(%rsp) #15.7
..LN69:
vzeroupper #15.7
..LN70:
call for_write_seq_lis #15.7
..LN71:
# LOE rbx r12 r13 r14 r15
..B1.7: # Preds ..B1.6
..LN72:
.loc 1 18 is_stmt 1
movl $1, %eax #18.1
..LN73:
movq %rbp, %rsp #18.1
..LN74:
popq %rbp #18.1
..___tag_value_MAIN__.6: #
..LN75:
ret #18.1
.align 16,0x90
..___tag_value_MAIN__.8: #
..LN76:
# LOE
..LN77:
# mark_end;
.type MAIN__,@function
.size MAIN__,.-MAIN__
..LNMAIN__.78:
.LNMAIN__:
.section .rodata, "a"
.align 8
.align 8
__NLITPACK_0.0.1:
.long 0x00000000,0x00000000
.align 4
__STRLITPACK_0.0.1:
.byte 48
.byte 1
.byte 1
.byte 0
.byte 0
.data
# -- End MAIN__
.section .rodata, "a"
.space 3, 0x00 # pad
.align 4
.L_2il0floatpacket.0:
.long 0x3f800000
.type .L_2il0floatpacket.0,@object
.size .L_2il0floatpacket.0,4
.data
.section .note.GNU-stack, ""
# End
i
), so essentially all the time is spent doing## set up ymm3 with 4 copies of 1.0/(1.0*i),
# and j = %edx = 0
..B1.5: do {
incl %edx # j++
vaddpd %ymm3, %ymm2, %ymm2 # ymm3 + ymm2 => ymm2
cmpl $10000000, %edx } while(j<10000000);
jb ..B1.5 # Prob 99%
vaddpd
will completely dominate the cost of everything outside the loop, so all that matters is that this inner-loop is executed 10k / 4 times. (note the add $4, %eax
/ cmp $10000, %eax
/ jb
, with a branch target back to before the inner loop.)
Without OpenMP:
#pragma openmp
, but using multiple accumulators for increased parallelism. Multiple add instructions can be in-flight at once, instead of having each one depend on the previous.## set up ymm3 with 4 copies of 1.0/(1.0*i),
..B1.4:
addl $32, %edx #10.12
vaddpd %ymm9, %ymm8, %ymm8 # ymm8 + ymm9 => ymm8
vaddpd %ymm7, %ymm9, %ymm7 # ymm7 + ymm9 => ymm7
vaddpd %ymm0, %ymm9, %ymm0 # ymm0 + ymm9 => ymm0
vaddpd %ymm1, %ymm9, %ymm1 # ...
vaddpd %ymm2, %ymm9, %ymm2
vaddpd %ymm3, %ymm9, %ymm3
vaddpd %ymm4, %ymm9, %ymm4
vaddpd %ymm5, %ymm9, %ymm5
cmpl $10000000, %edx
jb ..B1.4 # Prob 99%
# then combine the 8 vector accumulators down to one, and horizontal sum that.
vaddpd
s in flight at once, but the latency is only 3 cycles on Intel SnB/IvB (See Agner Fog's insn tables). You didn't say what microarchitecture you're using, but I could infer Sandybridge/Ivybridge from the fact that -xhost
uses AVX1 but not AVX2. (broadcast with vmovddup
/ vinsertf128
, rather than AVX2 vbroadcastsd %xmm9, %ymm9
)vaddpd
has a throughput of one per clock on pre-Skylake Intel CPUs, latency=3. This version is limited by throughput rather than latency, because of the increased instruction-level parallelism).