Re: [FFmpeg-devel] [PATCH 0/6] RISC-V initial ac3dsp

["Rémi Denis-Courmont" <remi@remlab.net>]

Le torstaina 15. kesäkuuta 2023, 16.57.18 EEST Lynne a écrit :
> Jun 15, 2023, 12:37 by shenpeiting@eswincomputing.com:
> > From: Shen Peiting <shenpeiting@eswincomputing.com>
> > 
> > We optimized the six interfaces of AC3 init by RVV, the optimized
> > performance was tested on the RISC-V ISA simulator--Spike, and the
> > results were attached to each commit.
> > 
> > shenpeiting (6):
> >  lavc/ac3dsp: RISC-V V ac3_exponent_min
> >  lavc/ac3dsp: RISC-V V float_to_fixed24
> >  lavc/ac3dsp: RISC-V V ac3_sum_square_butterfly_int32
> >  lavc/ac3dsp: RISC-V V ac3_sum_square_butterfly_float
> >  lavc/ac3dsp: RISC-V V ac3_compute_mantissa_size
> >  lavc/ac3dsp: RISC-V B ac3_extract_exponents
> >  
> >  libavcodec/ac3dsp.c            |   2 +
> >  libavcodec/ac3dsp.h            |   1 +
> >  libavcodec/riscv/Makefile      |   3 +
> >  libavcodec/riscv/ac3dsp_init.c |  60 +++++++++
> >  libavcodec/riscv/ac3dsp_rvb.S  |  42 ++++++
> >  libavcodec/riscv/ac3dsp_rvv.S  | 225 +++++++++++++++++++++++++++++++++
> >  6 files changed, 333 insertions(+)
> >  create mode 100644 libavcodec/riscv/ac3dsp_init.c
> >  create mode 100644 libavcodec/riscv/ac3dsp_rvb.S
> >  create mode 100644 libavcodec/riscv/ac3dsp_rvv.S
> 
> Could you implement checkasm for this? It shouldn't
> be more than a hundred lines, and there are examples,
> tests/checkasm/aacpsdsp.c being the most similar.
> Since CPUs with the needed extensions aren't released,
> we're not doing any FATE runs,

Well... I accept hardware donations (with regular USB-C power supply and 
passive cooling) to back what would be the third generation of RISC-V FATE 
instances.

Until R-V-V 1.0 hardware production substitutes unobtainium for silicium, I 
also accept Lichee Pi4A or equivalent hardware bundles, which would be able to 
run most (but definitely not all) of FFmpeg's RVV functions with a sizable 
amount of kludging.

> and so if the results don't
> match the C version, we'll end up with broken code once
> they do exist. And no one wants to debug someone else's
> assembly.
> 
> Those results look far too optimistic, and I'm guessing
> it's because they're using a theoretical huge vector size
> limit. Could you re-test with something more realistic,
> like 256-bit vectors, using checkasm --bench?

It could also be that Spike counts everything as one cycle, regardless of the 
group multipler, not (just) the vector size.

-- 
Rémi Denis-Courmont
http://www.remlab.net/



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