[opus] [PATCH] Optimize silk_warped_autocorrelation_FIX() for ARM NEON
Jean-Marc Valin
jmvalin at jmvalin.ca
Tue Feb 7 01:47:04 UTC 2017
Hi Linfeng,
On 06/02/17 07:18 PM, Linfeng Zhang wrote:
> This is a great idea. But the order (psEncC->shapingLPCOrder) can be
> configured to 12, 14, 16, 20 and 24 according to complexity parameter.
>
> It's hard to get a universal function to handle all these orders
> efficiently. Any suggestions?
I can think of two ways of handling larger orders. The obvious one is
simply to add an inner loop of the form:
for (i=0;i<order;i+=VECTOR_SIZE)
I think what may be more efficient is to simply have a small "order-N"
(N=4 or 8) kernel that not only computes the correlation of order N, but
then spits out the signal after the N-stage all-pass is applied. The
kernel would look like:
void autocorr_kernel4(int *corr, int *orig, int *input, int *output, int
len) {
/* Implement vectorized order-4 filter (could also be order 8)
as described in previous email and outputs the filtered signal.
*/
}
and then the full function would run the kernel multiple times and look
like:
void full_autocorr(int *corr, int *orig, int len, int order) {
int i;
int tmp[MAX_SIZE];
int *in = orig;
for (i=0;i<order;i+=4) {
autocorr_kernel4(corr+i, orig, in, tmp, len);
/* Make subsequent calls use the filtered signal as input. */
in = tmp;
}
}
I think the should not only reduce/eliminate the prologue/epilogue
problem, but it should also be more efficient since almost all vectors
processed would use the full size.
Maybe a third option (not sure it's a good idea, but still mentioning
it) would be to have a function that hardcodes order=24 and discards the
larger values that aren't needed. Since the smallest order seems to be
16, it wouldn't be much of a waste and the code might end up running
faster for the higher orders.
Cheers,
Jean-Marc
> Thanks,
> Linfeng
>
> On Mon, Feb 6, 2017 at 12:40 PM, Jean-Marc Valin <jmvalin at jmvalin.ca
> <mailto:jmvalin at jmvalin.ca>> wrote:
>
> Hi Linfeng,
>
> On 06/02/17 02:51 PM, Linfeng Zhang wrote:
> > However, the critical thing is that all the states in each stage when
> > processing input[i] are reused by the next input[i+1]. That is
> > input[i+1] must wait input[i] for 1 stage, and input[i+2] must wait
> > input[i+1] for 1 stage, etc.
>
> That is indeed the tricky part... and the one I think you could do
> slightly differently. If you approach the problem in terms of computing
> chunks of the inputs N samples at a time, then indeed the approach you
> are describing is the only solution. What I was proposing though is to
> instead chop the "order" in chunks of N. Using your notation, you would
> be doing:
>
> PROC( in0(s0))
> PROC( in0(s1) in1(s0))
> PROC( in0(s2) in1(s1) in2(s0))
> PROC( in0(s3) in1(s2) in2(s1) in3(s0))
> PROC( in0(s4) in1(s3) in2(s2) in3(s1) in4(s0))
> PROC( in0(s5) in1(s4) in2(s3) in3(s2) in4(s1) in5(s0))
> PROC( in0(s6) in1(s5) in2(s4) in3(s3) in4(s2) in5(s1) in6(s0))
> PROC(in0(s7) in1(s6) in2(s5) in3(s4) in4(s3) in5(s2) in6(s1) in7(s0))
> PROC(in1(s7) in2(s6) in3(s5) in4(s4) in5(s3) in6(s2) in7(s1) in8(s0))
> PROC(in2(s7) in3(s6) in4(s5) in5(s4) in6(s3) in7(s2) in8(s1) in9(s0))
> PROC(in3(s7) in4(s6) in5(s5) in6(s4) in7(s3) in8(s2) in9(s1)in10(s0))
> PROC(in4(s7) in5(s6) in6(s5) in7(s4) in8(s3) in9(s2)in10(s1)in11(s0))
> ...and so on until the end of the input vector
>
> The difference is that it's now the input vector that "slides" and the
> "state" values sy that remain in the same place. There's still a
> prologue, but you can easily get rid of it by (implicitly) zero-padding
> the in vector during the initialization phase (start with a zero vector
> and real one value at a time). Getting rid of the epilogue is a little
> trickier, but I think it can be done.
>
> Cheers,
>
> Jean-Marc
>
> > Then it becomes this
> >
> > FOR in=0 to N WITH in+=8
> > PROC(in0(s0)) /* prolog 0 */
> > PROC(in0(s1) in1(s0)) /* prolog 1 */
> > PROC(in0(s2) in1(s1) in2(s0)) /* prolog 2 */
> > PROC(in0(s3) in1(s2) in2(s1) in3(s0)) /* prolog 3 */
> > PROC(in0(s4) in1(s3) in2(s2) in3(s1) in4(s0)) /* prolog 4 */
> > PROC(in0(s5) in1(s4) in2(s3) in3(s2) in4(s1) in5(s0)) /* prolog 5 */
> > PROC(in0(s6) in1(s5) in2(s4) in3(s3) in4(s2) in5(s1) in6(s0)) /*
> > prolog 6 */
> > PROC(in0(s7) in1(s6) in2(s5) in3(s4) in4(s3) in5(s2) in6(s1)
> in7(s0))
> > /* fully process 8 inputs */
> > PROC(in0(s8) in1(s7) in2(s6) in3(s5) in4(s4) in5(s3) in6(s2)
> in7(s1))
> > /* continue */
> > PROC(in0(s9) in1(s8) in2(s7) in3(s6) in4(s5) in5(s4) in6(s3)
> in7(s2))
> > /* continue */
> > PROC(in0(s10) in1(s9) in2(s8) in3(s7) in4(s6) in5(s5) in6(s4)
> in7(s3))
> > /* continue */
> > PROC(in1(s10) in2(s9) in3(s8) in4(s7) in5(s6) in6(s5) in7(s4)) /*
> > epilog 0 */
> > PROC(in2(s10) in3(s9) in4(s8) in5(s7) in6(s6) in7(s5)) /* epilog
> 1 */
> > PROC(in3(s10) in4(s9) in5(s8) in6(s7) in7(s6)) /* epilog 2 */
> > PROC(in4(s10) in5(s9) in6(s8) in7(s7)) /* epilog 3 */
> > PROC(in5(s10) in6(s9) in7(s8)) /* epilog 4 */
> > PROC(in6(s10) in7(s9)) /* epilog 5 */
> > PROC(in7(s10)) /* epilog 6 */
> > END FOR
> >
> > And
> > PROC(in0(s7) in1(s6) in2(s5) in3(s4) in4(s3) in5(s2) in6(s1)
> in7(s0))
> > /* fully process 8 inputs */
> > PROC(in0(s8) in1(s7) in2(s6) in3(s5) in4(s4) in5(s3) in6(s2)
> in7(s1))
> > /* continue */
> > PROC(in0(s9) in1(s8) in2(s7) in3(s6) in4(s5) in5(s4) in6(s3)
> in7(s2))
> > /* continue */
> > is actually the expansion of the kernel loop
> > FOR i=0 TO order-6 WITH i++
> > PROC(in0(si+7) in1(si+6) in2(si+5) in3(si+4) in4(si+3) in5(si+2)
> > in6(si+1) in7(si+0))
> > END FOR
> >
> > The worst thing is that corr_QC[] is so sensitive that any extra
> > processing will make them wrong and propagate to the next loop (next 8
> > inputs). state_QS[] is a little better but still very sensitive. For
> > instance, if adding PROC(in0(s11') in1(s10) in2(s9) in3(s8) in4(s7)
> > in5(s6) in6(s5) in7(s4)) to the kernel loop (by looping one more time)
> > and remove epilog 0, then all final results will be wrong.
> >
> > That's why the prolog and epilog cannot be saved to the best of my
> > knowledge.
> >
> > The assembly size of silk_warped_autocorrelation_FIX_neon() is about
> > 2,744 bytes. Compared with the C code size (about 452 bytes), it's 2.3
> > KB larger. Considering silk_warped_autocorrelation_FIX_c() is the
> second
> > place CPU heavy function in fixed-point, and our testing shows up
> to 7%
> > CPU run time saving of the total encoder with this optimization (at
> > Complexity 8), maybe we can take the I-cache burden even if finally we
> > still cannot remove the big chunk of prolog and epilog.
> >
> > Thanks,
> > Linfeng Zhang
> >
> > On Sat, Feb 4, 2017 at 4:17 PM, Jean-Marc Valin
> <jmvalin at jmvalin.ca <mailto:jmvalin at jmvalin.ca>
> > <mailto:jmvalin at jmvalin.ca <mailto:jmvalin at jmvalin.ca>>> wrote:
> >
> > Hi Felicia,
> >
> > I've had time to work through the math in the original
> function and I'm
> > pretty sure it's possible to vectorize this without the huge
> > prologue/epilogue.
> >
> > For the simple case where order = vector size = N (but it
> should easily
> > generalize to larger order), what I came up with is:
> >
> > initialize X, Y, M, C to vector of zeros
> >
> > for i=0 to N+order
> > T = [x(i), Y(0:N-2)]
> > Y = M + coeff * (Y - T)
> > M = T
> > X = [x(i), X(0:N-1)]
> > C = C + X*Y
> >
> > I think something similar to this (assuming I didn't mess up any
> > details) should give you the correlations in vector C. Did I miss
> > anything?
> >
> > Cheers,
> >
> > Jean-Marc
> >
> >
> > On 31/01/17 12:30 PM, Felicia Lim wrote:
> > > Hi,
> > >
> > > Attached is a patch with arm neon optimizations for
> > > silk_warped_autocorrelation_FIX(). Please review.
> > >
> > > Thanks,
> > > Felicia
> > >
> > >
> > > _______________________________________________
> > > opus mailing list
> > > opus at xiph.org <mailto:opus at xiph.org> <mailto:opus at xiph.org
> <mailto:opus at xiph.org>>
> > > http://lists.xiph.org/mailman/listinfo/opus
> <http://lists.xiph.org/mailman/listinfo/opus>
> > <http://lists.xiph.org/mailman/listinfo/opus
> <http://lists.xiph.org/mailman/listinfo/opus>>
> > >
> > _______________________________________________
> > opus mailing list
> > opus at xiph.org <mailto:opus at xiph.org> <mailto:opus at xiph.org
> <mailto:opus at xiph.org>>
> > http://lists.xiph.org/mailman/listinfo/opus
> <http://lists.xiph.org/mailman/listinfo/opus>
> > <http://lists.xiph.org/mailman/listinfo/opus
> <http://lists.xiph.org/mailman/listinfo/opus>>
> >
> >
>
>
More information about the opus
mailing list