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

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Message-ID: <CAGsJ_4zPrgkb37VCfY+C8Dn6dS4LmSMrHnfU7Oy4bR19yhxbAA@mail.gmail.com>
Date: Fri, 21 Nov 2025 09:24:18 +0800
From: Barry Song <21cnbao@...il.com>
To: linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org, 
	linux-media@...r.kernel.org, sumit.semwal@...aro.org
Cc: Brian.Starkey@....com, benjamin.gaignard@...labora.com, 
	christian.koenig@....com, dri-devel@...ts.freedesktop.org, jstultz@...gle.com, 
	tjmercier@...gle.com, v-songbaohua@...o.com, zhengtangquan@...o.com, 
	marcin.slusarz@....com
Subject: Re: [PATCH v2] dma-buf: system_heap: use larger contiguous mappings
 instead of per-page mmap

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