RFR: 8238954: Improve performance of tiled snapshot rendering

[Frederic Thevenet]

On Tue, 10 Mar 2020 11:13:54 GMT, Frederic Thevenet <github.com+7450507+fthevenet at openjdk.org> wrote:

>> ### 15-internal:
>> 
>> --------
>> |    | 1024 |2048 |3072 |4096 |5120 |6144 |7168 |8192 |9216 |
>> |---|---|---|---|---|---|---|---|---|---|
>> | 1024 | 5.381051 | 9.261115 | 14.033219 | 20.608201 | 26.159817 | 33.599632 | 36.669261 | 43.042338 | 46.086088 |
>> | 2048 | 9.752862 | 17.698869 | 27.004541 | 38.437578 | 52.297443 | 60.757880 | 68.101838 | 80.162117 | 93.852856 |
>> | 3072 | 15.564961 | 27.304138 | 40.255866 | 56.636476 | 80.472402 | 86.346635 | 105.154089 | 121.048263 | 130.458981 |
>> | 4096 | 19.436113 | 35.556343 | 53.277865 | 71.623899 | 95.814932 | 122.543003 | 136.833771 | 160.199834 | 178.356125 |
>> | 5120 | 27.246498 | 65.875784 | 73.171492 | 103.380029 | 126.486761 | 147.666102 | 165.833885 | 199.005331 |
>> 220.659671 | | 6144 | 31.843301 | 62.101937 | 93.646729 | 125.531512 | 150.914608 | 175.553034 | 209.835003 |
>> 241.114596 | 253.512648 | | 7168 | 40.507918 | 70.843435 | 101.075064 | 137.284040 | 165.808501 | 197.015259 |
>> 254.286955 | 304.928104 | 299.992601 | | 8192 | 43.206941 | 80.290957 | 121.946965 | 157.016439 | 193.509481 |
>> 243.514969 | 268.151933 | 359.562281 | 352.102850 | | 9216 | 49.529493 | 90.895186 | 149.422784 | 179.512616 |
>> 217.260338 | 267.610592 | 309.706685 | 354.950852 | 383.275751 |
>> ![15-internal](https://user-images.githubusercontent.com/7450507/76303560-3a544480-62c2-11ea-9860-030a0110a9fe.png)
>
> I've uploaded 3 sets of results, from 3 different implementations:
> 
> 1. **14-ea+9** is the implementation merged into openjfx14 following #68; it only use tiling if the original
> implementation fails; on Windows that would typically be when the snapshot dimensions are larger than 8192 pixels.
> 2. **14-internal** uses the same tiling implementation than the above, but start using tiling as soon as snapshot
> dimensions are larger than `PrismSettings.maxTextureSize`; i.e. typically 4096 pixels.  NB: This implementation was
> never merged into openJFX; results are only provided for comparison's sake.
> 3. **15-internal** uses the tiling implementation proposed in the PR. Compared to the ones above, it attempt to align
> pixel formats to avoid the cost of transformation from one format to another (e.g. ByteBRGA to IntARGB) and it tries to
> divide up the final snapshots into tiles of the same dimensions to prevent creating a new GPU surface for every tile.
> **Please note that these results are for the best possible scenario with regard to the above optimizations; in the worst
>   case scenario (a user provided image with a different pixel format and no way to divide the snapshot into equal size
>   tiles), then the performances are the same as that of implementation 2**
> 
> My conclusions from the above results are twofold:
> 
> - Tiling has a cost in terms of performance, but as far as I can tell it remains the only practical way to work around
>   the underlying issue (i.e. taking snapshot larger than the supported texture size) and the optimizations proposed in
>   this PR arguably do mitigate that cost, even if it is only true in some of the cases.
> 
> - The original implementation, which is preserved in 14-ea+9, ignores texture clamping to 4096 which means it doesn't has
>   to resort to tiling until the target snapshot size is >8192 on d3d or 16384 on es2.
> If this is an incorrect behaviour on the part of the original implementation (which I'm led to believe is the case), it
> gives it an unfair advantage in this benchmark, i.e. it is faster because is does things it shouldn't do. If however it
> turns out it is actually safe to ignore clamping when taking snapshot, then it would make sense to do so in the
> implementation proposed by this PR as well.

By the way, the code for the above benchmark is available here: https://github.com/fthevenet/snapshot-perf-meter

Would it make sense to include it into the OpenJFX repo, maybe under jfx/apps/performance ?

-------------

PR: https://git.openjdk.java.net/jfx/pull/112