[opus] [PATCH] Optimize silk_warped_autocorrelation_FIX() for ARM NEON
Jean-Marc Valin
jmvalin at jmvalin.ca
Wed Apr 5 18:02:24 UTC 2017
Hi Linfeng,
Thanks for the updated patch. I'll have a look and get back to you. When
you report speedup percentages, is that relative to the entire encoder
or relative to just that function in C? Also, what's the speedup
compared to master?
Cheers,
Jean-Marc
On 05/04/17 12:14 PM, Linfeng Zhang wrote:
> I attached a new patch with small cleanup (disassembly is identical as
> the last patch). We have done the same internal testing as usual.
>
> Also, attached 2 failed temporary versions which try to reduce code size
> (just for code review reference purpose).
>
> The new patch of silk_warped_autocorrelation_FIX_neon() has a code size
> of 3,228 bytes (with gcc).
> smaller_slower.c has a code size of 2,304 bytes, but the encoder is
> about 1.8% - 2.7% slower.
> smallest_slowest.c has a code size of 1,656 bytes, but the encoder is
> about 2.3% - 3.6% slower.
>
> Thanks,
> Linfeng
>
> On Mon, Apr 3, 2017 at 3:01 PM, Linfeng Zhang <linfengz at google.com
> <mailto:linfengz at google.com>> wrote:
>
> Hi Jean-Marc,
>
> Attached is the silk_warped_autocorrelation_FIX_neon() which
> implements your idea.
>
> Speed improvement vs the previous optimization:
>
> Complexity 0-4: Doesn't call this function. Complexity 5: 2.1%
> (order = 16) Complexity 6: 1.0% (order = 20) Complexity 8: 0.1%
> (order = 24) Complexity 10: 0.1% (order = 24)
>
> Code size of silk_warped_autocorrelation_FIX_neon() changes from
> 2,644 bytes to 3,228 bytes.
>
> The reason of larger code size is that the new optimization
> specializes order 16, 20 and 24. If only keeping order 24
> specialization, the code still works and the code size is smaller,
> but the encoder speed will drop 4.0% for Complexity 5 and 2.0% for
> Complexity 6. Anyway, the new code is easier to understand and maintain.
>
> Thanks,
>
> Linfeng
>
>
> On Tue, Feb 7, 2017 at 8:58 AM, Linfeng Zhang <linfengz at google.com
> <mailto:linfengz at google.com>> wrote:
>
> Hi Jean-Marc,
>
> Thanks for your suggestions. Will get back to you once we have
> some updates.
>
> Linfeng
>
> On Mon, Feb 6, 2017 at 5:47 PM, Jean-Marc Valin
> <jmvalin at jmvalin.ca <mailto:jmvalin at jmvalin.ca>> wrote:
>
> 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>
> > <mailto: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>>
> > > <mailto: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
> > > >
> > > >
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