Cache partitioning

[Everaldo-Gomes]

Hi!
Can I get some guidance about how to configure / use cache partitioning in the hypervisor?

Platform: Raspberry Pi 4b
Demo: Dual-guest Linux+FreeRTOS

[Diogo21Costa]

Hi @Everaldo-Gomes,

The cache coloring can be configured using the colors field within the vm_config struct.

This field corresponds to a bitmap for the assigned cache colors of the VM. This value is truncated depending on the number of available colors calculated at run-time, i.e., it is platform-dependent. By default, the coloring mechanism is not active.

For instance, in your setup, you could assign 50% of cache colors to each VM by setting .colors=0b00001111 to Linux and .colors=0b11110000 to FreeRTOS.

Please feel free to let me know if you need any more help.

[Diogo21Costa]

You don't need to, all you need to do is to update your configuration file (e.g., if you're using the config file from bao demos you could add the following changes:

        { 
            .image = {
                .base_addr = 0x20000000,
                .load_addr = VM_IMAGE_OFFSET(linux_image),
                .size = VM_IMAGE_SIZE(linux_image)
            },

            .entry = 0x20000000,
+         .colors = 0b11110000,

            .platform = {

            .image = {
                .base_addr = 0x0,
                .load_addr = VM_IMAGE_OFFSET(freertos_image),
                .size = VM_IMAGE_SIZE(freertos_image)
            },

            .entry = 0x0,
+         .colors = 0b00001111,

            .platform = {

[Everaldo-Gomes]

Thank you so much!

[Everaldo-Gomes]

"Assign 50% of cache colors to each VM by setting .colors=0b00001111 to Linux and .colors=0b11110000 to FreeRTOS."
I believe it means that an amount of colors is already defined.

How can I define the number of colors?
Where can I find how the .colors=0b00001111 is transformed/mapped in the partitions?

Are these values related to 32 or 64 bits, and how do I know this?

[Diogo21Costa]

The allocation of cache colors to each VM is predetermined based on the architecture of the cache system. The number of cache partitions is determined by the structure of the cache, typically calculated as the way size divided by the page size. To confirm the number of colors available for a specific platform, one can check the variable COLOR_NUM, typically calculated at runtime for ARM-based platforms (please check this file).

Regarding the values specified in the assignment (0b00001111 for Linux and 0b11110000 for FreeRTOS), these are bitmasks indicating which cache colors each VM can utilize, where each bit corresponds to one color. These values are platform-specific and related to the size of the cache way (my example was for a zcu104). However, for the Raspberry Pi 4 platform, there are only four colors available. Therefore, for a 50/50 cache coloring scheme, the bitmask for Linux would be 0b1100, and for FreeRTOS, it would be 0b0011.

[Everaldo-Gomes]

Thanks for the detailed explanation, I appreciate it!