linux-kernel - Re: [PATCH] arm: exynos increase CONFIG_CMA_SIZE

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Date:   Tue, 28 Feb 2017 09:52:33 -0700
From:   Shuah Khan <shuahkh@....samsung.com>
To:     Javier Martinez Canillas <javier@....samsung.com>,
        linux@...linux.org.uk, kgene@...nel.org, krzk@...nel.org,
        arnd@...db.de, cw00.choi@...sung.com, rafael.j.wysocki@...el.com,
        robie@...tgohome.co.uk, b.zolnierkie@...sung.com,
        viresh.kumar@...aro.org, m.szyprowski@...sung.com,
        s.nawrocki@...sung.com, a.hajda@...sung.com, inki.dae@...sung.com,
        sw0312.kim@...sung.com
Cc:     shuah@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH] arm: exynos increase CONFIG_CMA_SIZE_MBYTES to 96

On 02/28/2017 09:42 AM, Javier Martinez Canillas wrote:
> Hello Shuah,
> 
> The subject line isn't consistent with what's used for exynos_defconfig
> changes, please use instead:
> 
> ARM: exynos_defconfig: Increase CONFIG_CMA_SIZE_MBYTES to 96
> 

oops - I meant o make it exynos_defconfig

> On 02/27/2017 09:23 PM, Shuah Khan wrote:
>> Current CMA size of 64 Mbytes is right on the edge of being too small
>> for some display managers.  With the proposed s5p_mfc patch series that
>> pre-allocate buffers, when display manager starts, it fails to get GEM
>> buffers.  Increasing the CMA size to 96 solves the problem.
>>
>> Change CONFIG_CMA_SIZE_MBYTES to 96 in exynos_defconfig to address the
>> problem.
>>
> 
> As you mention, the problem is when a driver pre-allocates a lot of CMA
> memory. So instead of mentioning an in-flight patch series, I would make
> the commit message more generic. Something along the following lines:

I thought about making it generic and decided to mention the problem I am
seeing, so there is a context to it. Without this patch, some display
managers will see regression.

> 
> Current CMA size is 64 Mbytes, but this may not be enough if different
> drivers need to allocate big memory chunks.
> 
> For example, the s5p-mfc driver may need to do a pre-allocation of N MiB
> to decode a H.264 1080p video, and there won't be enough CMA memory left
> for others drivers, like the exynos-drm driver that may need to allocate
> GEM buffers for the display manager.
> 
> Increasing the CMA size to 96 MiB should be enough for most use cases.

I will add the current problem to throw away section of the patch for more
information.

> 
>> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
>> Suggested-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> ---
> 
> Patch looks good to me though.
> 
> Reviewed-by: Javier Martinez Canillas <javier@....samsung.com>

thanks for the review. I will send v2 with your reviewed by tag
> 
> Best regards,
> 

-- Shuah