Re: [PATCH v5 12/13] xen/arm: add Xen cache colors command line parameter

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 5 Jan 2024, Julien Grall wrote:
> Hi,
> 
> On 02/01/2024 09:51, Carlo Nonato wrote:
> > From: Luca Miccio <lucmiccio@xxxxxxxxx>
> > 
> > This commit adds a new command line parameter to configure Xen cache colors.
> > These colors can be dumped with the cache coloring info debug-key.
> > 
> > By default, Xen uses the first color.
> > 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.
> 
> Would you be able to share some numbers? This is quite helpful if in the
> future we need to revise the default.

Here are the numbers for Xen 1 color vs Xen 2 colors.

We are measuring IRQ lantecy using a baremetal app (a unikernel) that
has 0.5 us latency on native without interference.

Running the same application on Xen with 3 interference agents (3 other
VMs that keep thrashing the cache):

- Xen 1 color latency:  3.1 us
- Xen 2 color2 latency: 3.1 us

Attachment: Cache Coloring Xen Summit.pdf
Description: Adobe PDF document