Re: [PATCH v2] dma-buf: system_heap: use larger contiguous mappings instead of per-page mmap

[Barry Song]

Hi Sumit,

>
> Using the micro-benchmark below, we see that mmap becomes
> 3.5X faster:


Marcin pointed out to me off-tree that it is actually 35x faster,
not 3.5x faster. Sorry for my poor math. I assume you can fix this
when merging it?

>
> W/ patch:
>
> ~ # ./a.out
> mmap 512MB took 200266.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 198151.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 197069.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 196781.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 198102.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 195552.000 us, verify OK
>
> W/o patch:
>
> ~ # ./a.out
> mmap 512MB took 6987470.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 6970739.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 6984383.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 6971311.000 us, verify OK
> ~ # ./a.out
> mmap 512MB took 6991680.000 us, verify OK


Thanks
Barry