etnaviv: Beware of the PULSE_EATER

[Chris Healy]

Wow, that's a pretty big difference!

Did you by any chance test with the i.MX6 with GC2000 too?  It would be
interesting to see if there was a similar performance degradation as well
as what the absolute difference is between the GC2000 and GC3000 platforms.

Also, with regard to the OCRAM, can you specify which OCRAM was used?  (Did
you stick to the 2 128KB OCRAM hanging off MX6FAST2 or was the 1 256KB
OCRAM hanging off MX6FAST3 also used?  The 2 128KB OCRAM hanging off
MX6FAST2 should have the highest OCRAM performance.)

On Sun, Dec 11, 2016 at 8:27 AM, Wladimir J. van der Laan <laanwj at gmail.com>
wrote:

>
> 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)
>
> 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
>
>
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