etnaviv: Beware of the PULSE_EATER

[Christian Gmeiner]

Hi Wladimir,

>
> Entirly deserving of its B-horror name it does unspeakable
> things to performance if not set up correctly.
>
> I was doing memory benchmarks and noticed a serious discrepancy
> between running the same CL program with the Vivante driver
> and replaying it on etnaviv.
>
> After carefully comparing the registers written at initialization
> with both kernel drivers, it became apparent that the etnaviv
> DRM driver is not setting up register 0x0010C. Adding a single line
> at the end of etnaviv_gpu_init sped up pure-read performance from shaders by
> 7.5x and write performance by 1.5x:
>
>         gpu_write(gpu, VIVS_PM_PULSE_EATER, 0x015d0880);
>
> (instead of this line we likely want to replicate viv_gpu's per-model logic)
>

Yeah..

> Apart from silly CL benchmarks, I expect this to make a large impact with
> texturing and alpha blending as well. Exact results for i.MX6qp (GC3000) below.
>
> Wladimir
>
> ("readacc" does read-and-accumulate into register, "read" does only reads, "write"
> does only writes, "ram" benchmarks DDR3 RAM, "ocram" i.MX6 onchip ram)
>
> kernel 4.8.4 + etnaviv
> ----------------------
>
> Version: 1.0.0
>   Name: etnaviv
>   Date: 20151214
>   Description: etnaviv DRM
> [read]    [ram]   Speed:  15.395 MB/s
> [readacc] [ram]   Speed:  14.680 MB/s (compare to readacc4x_alt.cl below :( )
> [write]   [ram]   Speed: 148.453 MB/s (compare to write4x_alt.cl below :( )
> [read]    [ocram] Speed:  15.097 MB/s
> [readacc] [ocram] Speed:  14.367 MB/s
> [write]   [ocram] Speed: 148.419 MB/s
>
> kernel 4.1.5 + viv_gpu
> ----------------------
>
> [ram]
> (no bench_read.cl: pure reads are optimized away by CL compiler)
> Program: bench_readacc4x_alt.cl    Speed:  83.720 MB/s
> Program: bench_write4x_alt.cl      Speed: 234.708 MB/s
>
> etnaviv 4.8.4 after PULSE_EATER neutered
> ------------------------------------------
>
> Version: 1.0.0
>   Name: etnaviv
>   Date: 20151214
>   Description: etnaviv DRM
> [read]    [ram]   Speed: 113.414 MB/s
> [readacc] [ram]   Speed:  82.395 MB/s (comparable to readacc4x_alt.cl above)
> [write]   [ram]   Speed: 234.955 MB/s (comparable to write4x_alt.cl above)
> [read]    [ocram] Speed:  87.912 MB/s
> [readacc] [ocram] Speed:  70.329 MB/s
> [write]   [ocram] Speed: 234.956 MB/s
>

Cool... just send out kernel patches and put some benchmark results
into the cover letter.
And do not forget to remove the pulse eater TODO in etnaviv_gpu.c :)

greets
--
Christian Gmeiner, MSc

https://soundcloud.com/christian-gmeiner