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

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Message-ID: <20170228171925.wwr66u4k4vdqg27z@kozik-lap>
Date:   Tue, 28 Feb 2017 19:19:25 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Shuah Khan <shuahkh@....samsung.com>
Cc:     Javier Martinez Canillas <javier@....samsung.com>,
        linux@...linux.org.uk, kgene@...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, shuah@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm: exynos increase CONFIG_CMA_SIZE_MBYTES to 96

On Tue, Feb 28, 2017 at 09:52:33AM -0700, Shuah Khan wrote:
> 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

While at it, please put Suggested-by before Sob tag (let's say
chronological order).


Best regards,
Krzysztof