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

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 05/01/2024 23:09, Stefano Stabellini wrote:
> 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
Thanks for sharing the numbers. Would it be possible to include them in 
the commit message?
Cheers,

--
Julien Grall