Re: [PATCH v8 11/13] xen/arm: add Xen cache colors command line parameter

[Jan Beulich <jbeulich@suse.com>]

On 02.05.2024 18:55, Carlo Nonato wrote:
> From: Luca Miccio <lucmiccio@gmail.com>
> 
> Add a new command line parameter to configure Xen cache colors.
> These colors are dumped together with other coloring info.
> 
> Benchmarking the VM interrupt response time provides an estimation of
> LLC usage by Xen's most latency-critical runtime task. Results on Arm
> Cortex-A53 on Xilinx Zynq UltraScale+ XCZU9EG show that one color, which
> reserves 64 KiB of L2, is enough to attain best responsiveness:
> - Xen 1 color latency:  3.1 us
> - Xen 2 color latency:  3.1 us
> 
> Since this is the most common target for Arm cache coloring, the default
> amount of Xen colors is set to one.
> 
> More colors are instead very likely to be needed on processors whose L1
> cache is physically-indexed and physically-tagged, such as Cortex-A57.
> In such cases, coloring applies to L1 also, and there typically are two
> distinct L1-colors. Therefore, reserving only one color for Xen would
> senselessly partitions a cache memory that is already private, i.e.
> underutilize it.
> 
> Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
> Signed-off-by: Marco Solieri <marco.solieri@minervasys.tech>
> Signed-off-by: Carlo Nonato <carlo.nonato@minervasys.tech>

Reviewed-by: Jan Beulich <jbeulich@suse.com>