linux-kernel - Re: 3.15.4 runs *significantly* slower than 3.15.3 on iMX233 CPU

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Date:	Mon, 7 Jul 2014 12:42:23 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Manuel Reimer <Manuel.Spam@...fuerspam.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 3.15.4 runs *significantly* slower than 3.15.3 on iMX233 CPU

On Mon, Jul 07, 2014 at 09:29:21PM +0200, Manuel Reimer wrote:
> On 07/07/2014 09:14 PM, Guenter Roeck wrote:
> >Are you sure this did not just happen when you booted the new kernel
> >for the first time ? I have seen similar behavior with some distributions.
> 
> I did some more tries and found out that I had disabled some of my
> patches until I reached 3.15.4 (latest version) where I decided to
> do needed modifications to get my patches back in.
> 
> I tracked the problem down to the following patch:
> 
> 
> diff --git a/arch/arm/boot/dts/imx23-olinuxino.dts
> b/arch/arm/boot/dts/imx23-olinuxino.dts
> index d107c4a..993da2e 100644
> --- a/arch/arm/boot/dts/imx23-olinuxino.dts
> +++ b/arch/arm/boot/dts/imx23-olinuxino.dts
> @@ -64,7 +64,14 @@
>  				compatible = "fsl,imx23-spi";
>  				pinctrl-names = "default";
>  				pinctrl-0 = <&spi2_pins_a>;
> +				clock-frequency = <1000000>;

If I understand the code correctly, that means you reduce the access speed
for SPI flashes from 160 MHz down to 1 MHz.

If so, and if your system loads anything from a SPI flash, I would not be too
surprised that your system is now a bit on the slow side.

Guenter
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