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armv6: Accelerate ff_fft_calc for general case (nbits != 4) 

The previous implementation targeted DTS Coherent Acoustics, which only
requires nbits == 4 (fft16()). This case was (and still is) linked directly
rather than being indirected through ff_fft_calc_vfp(), but now the full
range from radix-4 up to radix-65536 is available. This benefits other codecs
such as AAC and AC3.

The implementaion is based upon the C version, with each routine larger than
radix-16 calling a hierarchy of smaller FFT functions, then performing a
post-processing pass. This pass benefits a lot from loop unrolling to
counter the long pipelines in the VFP. A relaxed calling standard also
reduces the overhead of the call hierarchy, and avoiding the excessive
inlining performed by GCC probably helps with I-cache utilisation too.

I benchmarked the result by measuring the number of gperftools samples that
hit anywhere in the AAC decoder (starting from aac_decode_frame()) or
specifically in the FFT routines (fft4() to fft512() and pass()) for the
same sample AAC stream:

              Before          After
              Mean   StdDev   Mean   StdDev  Confidence  Change
Audio decode  2245.5 53.1     1599.6 43.8    100.0%      +40.4%
FFT routines  940.6  22.0     348.1  20.8    100.0%      +170.2%

Signed-off-by: Martin Storsjö <martin@martin.st>
This commit is contained in:
Ben Avison 2014-07-16 16:02:01 +01:00 committed by Martin Storsjö
parent 5c22e8e4ad
commit 87552d54d3
2 changed files with 256 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
libavcodec/arm/fft_init_arm.c
View File

@ -23,6 +23,8 @@
#include "libavcodec/rdft.h"
#include "libavcodec/synth_filter.h"
void ff_fft_calc_vfp(FFTContext *s, FFTComplex *z);
void ff_fft_permute_neon(FFTContext *s, FFTComplex *z);
void ff_fft_calc_neon(FFTContext *s, FFTComplex *z);
@ -38,10 +40,10 @@ av_cold void ff_fft_init_arm(FFTContext *s)
{
int cpu_flags = av_get_cpu_flags();
if (have_vfp(cpu_flags)) {
if (have_vfp(cpu_flags) && !have_vfpv3(cpu_flags)) {
s->fft_calc = ff_fft_calc_vfp;
#if CONFIG_MDCT
if (!have_vfpv3(cpu_flags))
s->imdct_half = ff_imdct_half_vfp;
s->imdct_half = ff_imdct_half_vfp;
#endif
}

266
libavcodec/arm/fft_vfp.S
View File

@ -21,8 +21,39 @@
#include "libavutil/arm/asm.S"
@ TODO: * FFTs wider than 16
@ * dispatch code
@ The fftx_internal_vfp versions of the functions obey a modified AAPCS:
@ VFP is in RunFast mode, vector length 4, stride 1 thoroughout, and
@ all single-precision VFP registers may be corrupted on exit. The a2
@ register may not be clobbered in these functions, as it holds the
@ stored original FPSCR.
function ff_fft_calc_vfp, export=1
ldr ip, [a1, #0] @ nbits
mov a1, a2
A ldr pc, [pc, ip, lsl #2]
A .word 0
A .word 0
A .word 0
T movrel a2, (fft_tab_vfp - 8)
T ldr pc, [a2, ip, lsl #2]
T endfunc
T const fft_tab_vfp
.word fft4_vfp
.word fft8_vfp
.word X(ff_fft16_vfp) @ this one alone is exported
.word fft32_vfp
.word fft64_vfp
.word fft128_vfp
.word fft256_vfp
.word fft512_vfp
.word fft1024_vfp
.word fft2048_vfp
.word fft4096_vfp
.word fft8192_vfp
.word fft16384_vfp
.word fft32768_vfp
.word fft65536_vfp
A endfunc
function fft4_vfp
vldr d0, [a1, #0*2*4] @ s0,s1 = z[0]
@ -131,18 +162,22 @@ endfunc
vstr d9, [a1, #3 * 2*4]
.endm
function .Lfft8_internal_vfp
macro_fft8_head
macro_fft8_tail
bx lr
endfunc
function fft8_vfp
ldr a3, =0x03030000 @ RunFast mode, vector length 4, stride 1
fmrx a2, FPSCR
fmxr FPSCR, a3
vpush {s16-s31}
macro_fft8_head
macro_fft8_tail
mov ip, lr
bl .Lfft8_internal_vfp
vpop {s16-s31}
fmxr FPSCR, a2
bx lr
bx ip
endfunc
.align 3
@ -153,12 +188,7 @@ cos1pi8: @ cos(1*pi/8) = sqrt(2+sqrt(2))/2
cos3pi8: @ cos(2*pi/8) = sqrt(2-sqrt(2))/2
.float 0.3826834261417388916015625
function ff_fft16_vfp, export=1
ldr a3, =0x03030000 @ RunFast mode, vector length 4, stride 1
fmrx a2, FPSCR
fmxr FPSCR, a3
vpush {s16-s31}
function .Lfft16_internal_vfp
macro_fft8_head
@ FFT4(z+8)
vldr d10, [a1, #8 * 2*4]
@ -292,7 +322,213 @@ function ff_fft16_vfp, export=1
vstr d8, [a1, #0 * 2*4]
vstr d9, [a1, #4 * 2*4]
vpop {s16-s31}
fmxr FPSCR, a2
bx lr
endfunc
function ff_fft16_vfp, export=1
ldr a3, =0x03030000 @ RunFast mode, vector length 4, stride 1
fmrx a2, FPSCR
fmxr FPSCR, a3
vpush {s16-s31}
mov ip, lr
bl .Lfft16_internal_vfp
vpop {s16-s31}
fmxr FPSCR, a2
bx ip
endfunc
.macro pass n, z0, z1, z2, z3
add v6, v5, #4*2*\n
@ TRANSFORM_ZERO(z[0],z[o1],z[o2],z[o3])
@ TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1])
@ TRANSFORM(z[0],z[o1],z[o2],z[o3],wre[0],wim[0])
@ TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1])
vldr d8, [\z2, #8*(o2+1)] @ s16,s17
vldmdb v6!, {s2}
vldr d9, [\z3, #8*(o3+1)] @ s18,s19
vldmia v5!, {s0,s1} @ s0 is unused
vldr s7, [\z2, #8*o2] @ t1
vmul.f s20, s16, s2 @ vector * scalar
vldr s0, [\z3, #8*o3] @ t5
vldr s6, [\z2, #8*o2+4] @ t2
vldr s3, [\z3, #8*o3+4] @ t6
vmul.f s16, s16, s1 @ vector * scalar
ldr a4, =\n-1
1: add \z0, \z0, #8*2
.if \n*4*2 >= 512
add \z1, \z1, #8*2
.endif
.if \n*4*2 >= 256
add \z2, \z2, #8*2
.endif
.if \n*4*2 >= 512
add \z3, \z3, #8*2
.endif
@ up to 2 stalls (VFP vector issuing / waiting for s0)
@ depending upon whether this is the first iteration and
@ how many add instructions are inserted above
vadd.f s4, s0, s7 @ t5
vadd.f s5, s6, s3 @ t6
vsub.f s6, s6, s3 @ t4
vsub.f s7, s0, s7 @ t3
vldr d6, [\z0, #8*0-8*2] @ s12,s13
vadd.f s0, s16, s21 @ t1
vldr d7, [\z1, #8*o1-8*2] @ s14,s15
vsub.f s1, s18, s23 @ t5
vadd.f s8, s4, s12 @ vector + vector
@ stall (VFP vector issuing)
@ stall (VFP vector issuing)
@ stall (VFP vector issuing)
vsub.f s4, s12, s4
vsub.f s5, s13, s5
vsub.f s6, s14, s6
vsub.f s7, s15, s7
vsub.f s2, s17, s20 @ t2
vadd.f s3, s19, s22 @ t6
vstr d4, [\z0, #8*0-8*2] @ s8,s9
vstr d5, [\z1, #8*o1-8*2] @ s10,s11
@ stall (waiting for s5)
vstr d2, [\z2, #8*o2-8*2] @ s4,s5
vadd.f s4, s1, s0 @ t5
vstr d3, [\z3, #8*o3-8*2] @ s6,s7
vsub.f s7, s1, s0 @ t3
vadd.f s5, s2, s3 @ t6
vsub.f s6, s2, s3 @ t4
vldr d6, [\z0, #8*1-8*2] @ s12,s13
vldr d7, [\z1, #8*(o1+1)-8*2] @ s14,s15
vldr d4, [\z2, #8*o2] @ s8,s9
vldmdb v6!, {s2,s3}
vldr d5, [\z3, #8*o3] @ s10,s11
vadd.f s20, s4, s12 @ vector + vector
vldmia v5!, {s0,s1}
vldr d8, [\z2, #8*(o2+1)] @ s16,s17
@ stall (VFP vector issuing)
vsub.f s4, s12, s4
vsub.f s5, s13, s5
vsub.f s6, s14, s6
vsub.f s7, s15, s7
vmul.f s12, s8, s3 @ vector * scalar
vstr d10, [\z0, #8*1-8*2] @ s20,s21
vldr d9, [\z3, #8*(o3+1)] @ s18,s19
vstr d11, [\z1, #8*(o1+1)-8*2] @ s22,s23
vmul.f s8, s8, s0 @ vector * scalar
vstr d2, [\z2, #8*(o2+1)-8*2] @ s4,s5
@ stall (waiting for s7)
vstr d3, [\z3, #8*(o3+1)-8*2] @ s6,s7
vmul.f s20, s16, s2 @ vector * scalar
@ stall (VFP vector issuing)
@ stall (VFP vector issuing)
@ stall (VFP vector issuing)
vadd.f s7, s8, s13 @ t1
vsub.f s6, s9, s12 @ t2
vsub.f s0, s10, s15 @ t5
vadd.f s3, s11, s14 @ t6
vmul.f s16, s16, s1 @ vector * scalar
subs a4, a4, #1
bne 1b
@ What remains is identical to the first two indentations of
@ the above, but without the increment of z
vadd.f s4, s0, s7 @ t5
vadd.f s5, s6, s3 @ t6
vsub.f s6, s6, s3 @ t4
vsub.f s7, s0, s7 @ t3
vldr d6, [\z0, #8*0] @ s12,s13
vadd.f s0, s16, s21 @ t1
vldr d7, [\z1, #8*o1] @ s14,s15
vsub.f s1, s18, s23 @ t5
vadd.f s8, s4, s12 @ vector + vector
vsub.f s4, s12, s4
vsub.f s5, s13, s5
vsub.f s6, s14, s6
vsub.f s7, s15, s7
vsub.f s2, s17, s20 @ t2
vadd.f s3, s19, s22 @ t6
vstr d4, [\z0, #8*0] @ s8,s9
vstr d5, [\z1, #8*o1] @ s10,s11
vstr d2, [\z2, #8*o2] @ s4,s5
vadd.f s4, s1, s0 @ t5
vstr d3, [\z3, #8*o3] @ s6,s7
vsub.f s7, s1, s0 @ t3
vadd.f s5, s2, s3 @ t6
vsub.f s6, s2, s3 @ t4
vldr d6, [\z0, #8*1] @ s12,s13
vldr d7, [\z1, #8*(o1+1)] @ s14,s15
vadd.f s20, s4, s12 @ vector + vector
vsub.f s4, s12, s4
vsub.f s5, s13, s5
vsub.f s6, s14, s6
vsub.f s7, s15, s7
vstr d10, [\z0, #8*1] @ s20,s21
vstr d11, [\z1, #8*(o1+1)] @ s22,s23
vstr d2, [\z2, #8*(o2+1)] @ s4,s5
vstr d3, [\z3, #8*(o3+1)] @ s6,s7
.endm
.macro def_fft n, n2, n4
function .Lfft\n\()_internal_vfp
.if \n >= 512
push {v1-v6,lr}
.elseif \n >= 256
push {v1-v2,v5-v6,lr}
.else
push {v1,v5-v6,lr}
.endif
mov v1, a1
bl .Lfft\n2\()_internal_vfp
add a1, v1, #8*(\n/4)*2
bl .Lfft\n4\()_internal_vfp
movrelx v5, X(ff_cos_\n), a1
add a1, v1, #8*(\n/4)*3
bl .Lfft\n4\()_internal_vfp
.if \n >= 512
.set o1, 0*(\n/4/2)
.set o2, 0*(\n/4/2)
.set o3, 0*(\n/4/2)
add v2, v1, #8*2*(\n/4/2)
add v3, v1, #8*4*(\n/4/2)
add v4, v1, #8*6*(\n/4/2)
pass (\n/4/2), v1, v2, v3, v4
pop {v1-v6,pc}
.elseif \n >= 256
.set o1, 2*(\n/4/2)
.set o2, 0*(\n/4/2)
.set o3, 2*(\n/4/2)
add v2, v1, #8*4*(\n/4/2)
pass (\n/4/2), v1, v1, v2, v2
pop {v1-v2,v5-v6,pc}
.else
.set o1, 2*(\n/4/2)
.set o2, 4*(\n/4/2)
.set o3, 6*(\n/4/2)
pass (\n/4/2), v1, v1, v1, v1
pop {v1,v5-v6,pc}
.endif
endfunc
function fft\n\()_vfp
ldr a3, =0x03030000 /* RunFast mode, vector length 4, stride 1 */
fmrx a2, FPSCR
fmxr FPSCR, a3
vpush {s16-s31}
mov ip, lr
bl .Lfft\n\()_internal_vfp
vpop {s16-s31}
fmxr FPSCR, a2
bx ip
endfunc
.ltorg
.endm
def_fft 32, 16, 8
def_fft 64, 32, 16
def_fft 128, 64, 32
def_fft 256, 128, 64
def_fft 512, 256, 128
def_fft 1024, 512, 256
def_fft 2048, 1024, 512
def_fft 4096, 2048, 1024
def_fft 8192, 4096, 2048
def_fft 16384, 8192, 4096
def_fft 32768, 16384, 8192
def_fft 65536, 32768, 16384