linux-kernel - Re: [PATCH v2] staging: vc04_services: Replace dmac_map_area with dmac_map

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Date:   Wed, 26 Oct 2016 17:57:24 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Michael Zoran <mzoran@...wfest.net>, gregkh@...uxfoundation.org
Cc:     swarren@...dotorg.org, lee@...nel.org, daniels@...labora.com,
        noralf@...nnes.org, mzoran@...wfest.net, popcornmix@...il.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] staging: vc04_services: Replace dmac_map_area with dmac_map_sg

Michael Zoran <mzoran@...wfest.net> writes:

> The original arm implementation uses dmac_map_area which is not
> portable.  Replace it with an architecture neutral version
> which uses dma_map_sg.
>
> As you can see that for larger page sizes, the dma_map_sg
> implementation is faster then the original unportable dma_map_area
> implementation.
>
> Test                       dmac_map_area   dma_map_page dma_map_sg
> vchiq_test -b 4 10000      51us/iter       76us/iter    76us
> vchiq_test -b 8 10000      70us/iter       82us/iter    91us
> vchiq_test -b 16 10000     94us/iter       118us/iter   121us
> vchiq_test -b 32 10000     146us/iter      173us/iter   187us
> vchiq_test -b 64 10000     263us/iter      328us/iter   299us
> vchiq_test -b 128 10000    529us/iter      631us/iter   595us
> vchiq_test -b 256 10000    2285us/iter     2275us/iter  2001us
> vchiq_test -b 512 10000    4372us/iter     4616us/iter  4123us

Reviewed-by: Eric Anholt <eric@...olt.net>

Nice work!  More portability and better performance at the same time.

A possible future improvement would be to track the pagelist, num_pages,
and pagelist_size in a struct in the bulk->remote_data so we didn't need
to recalculate them at free time.

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