When DRAM is idle the system I have is putting the DRAM modules in a power down/self refresh mode and no clock is sent to the DRAM. This is causing issues with a debugging tool I have attached to the memory.

I would like to know if/how this feature can be disabled from within Linux or the Kernel as it does not seem to happen if the machine is paused at boot stage.

Not sure but I think there is a kernel option for RAM power management that can be turned off in kernel config.

I am running kernel 3.16.6 and cannot find anything that makes a difference with make xconfig. There is an Intel specific option CONFIG_I7300_IDLE which makes no difference on the Supermicro Opteron based board I have.

There are some files in /sys/devices/system/memory/, is this where the self refresh mode can be disabled?

Hi,

Welcome to LQ!

I suggest that you look at; https://en.wikipedia.org/wiki/Memory_controller so that you can understand the memory management process.

Look at; https://en.wikipedia.org/wiki/Dynami...-access_memory to get an understanding how DRAM functions with a system.

Hope this helps.
Have fun & enjoy!

My understanding is that there is a defined sequence for powering down a DRAM module called a POWER DOWN ENTRY. This consists of removing clock enable, CKE, while the chip is still selected CS#. After that the clock is removed. This can be actioned by setting the EnterSelfRef bit in the DRAM configuration low register, for an AMD Opteron.

Something somewhere must be doing this, or something similar, or is the result of some other function. Whatever the source is, it would seem Linux has a role to play as it does not seem to happen if Linux is not booted.

For anyone that is interested I did find a solution to my problem.

By adding idle=poll to the kernel boot options you can stop this power saving mode. I am not suggesting it would be something of any value to anyone else but it did what I wanted.

vmhb,
I don't mind if I do, mine's a double old chap!