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

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Date:	Mon, 07 Jul 2014 21:29:21 +0200
From:	Manuel Reimer <Manuel.Spam@...fuerspam.de>
To:	linux-kernel@...r.kernel.org
Subject: Re: 3.15.4 runs *significantly* slower than 3.15.3 on iMX233 CPU

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>;
  				status = "okay";
+
+				spidev0: spidev@0 {
+					compatible = "spidev";
+					spi-max-frequency = <1000000>;
+					reg = <0>;
+				};
  			};
  		};


I need this to add spidev support. But I don't understand why this 
change kills performance? Maybe the "high" value in "clock-frequency"? 
Can someone give me some information on how to fix this?

Thank you very much in advance.

Greetings,

Manuel

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