Slow down with recent linux kernel

Slow down with recent linux kernel

[Richard Laing]

We are developing a new Linux based product on custom hardware (mpc855 CPU). We are currently running the 2.4.22 kernel (straight from kernel.org). This works fine. We would like to move to the latest 2.4.25 kernel but although the kernel compiles and runs it runs much slower than the 2.4.22 kernel. Startup time for our application form power on to running is increased by between 30% and 50%. Has anyone else seen anything like this or has anyone any idea where to start looking for the cause of this slow down.

The serial console works correctly with both kernels with apparent speed change.

We have DRAM, Flash (incuding a JFFS2 file system), I2C and SPI devices.

Also...the latest kernel breaks our SPI driver since alloc_host_memory is used to allocate the host_buffer pointer, this uses consistent_alloc which doesn't appear to return a real physical address which means that memory allocated using m8xx_cpm_hostalloc cannot be used as a buffer pointer for SPI transactions. Is there another way to get real memory? Currently I have reverted some of the commproc.c code to use the host_page_address as in the 2.4.22 kernel. Is this a possible source of the slow down?

Regards
Richard Laing

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Re: Slow down with recent linux kernel

[Dan Malek]

Richard Laing wrote:

> ....Startup time for our application form power on to running is increased
 > by between 30% and 50%.

How does your application start up?  Initrd? Jffs2? Network?
What are you actually measuring?

Use some standard, focused, benchmarks and collect some quantitative data.
Then, we can discuss something.

> ....this uses consistent_alloc which doesn't appear to return a
 > real physical address

Sure it does....dma_addr_t.

Thanks.


	-- Dan


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FCC Ethernet MDIO interface

[Jos Beck]

Dear Dan,

We are trying to use U-boot for a new MPC8250 circuit.
When looking at cpu/mpc8260/ether_fcc.c I cannot find any reference to
the control of the MDC and MDIO lines of the MII interface to the PHY.

Where can I find the code that controls MDIO? (e.g. to defive which CPM
pins are used)
Is the MDIO interface used/supported anyhow in u-boot or the kernel?


Best Regards,

Jos Beck


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Re: FCC Ethernet MDIO interface

[Dan Malek]

First of all, this should be posted on the u-boot mailing list, not here.

Jos Beck wrote:

> We are trying to use U-boot for a new MPC8250 circuit.

> Where can I find the code that controls MDIO? (e.g. to defive which CPM
> pins are used)

If you take a look at some other 8260 derivative boards, it's kinda
obvious how it is done.  First CONFIG_MII, CONFIG_BITBANGMII.  Define
the macros for MDIO, MDC, and MIIDELAY specific to your implementation.
Due to the wide variation of implementation, the PHY management is done
from the board specific files, not in the generic FCC driver.  Take a
look at board/mpc8260ads/mpc8260ads.c.

> Is the MDIO interface used/supported anyhow in u-boot or the kernel?

Yes, in many different variations that you can model to suit your needs.


	-- Dan


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