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Re: [PATCH v8 11/13] xen/arm: add Xen cache colors command line parameter
- To: Carlo Nonato <carlo.nonato@xxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 6 May 2024 15:24:50 +0200
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- Cc: andrea.bastoni@xxxxxxxxxxxxxxx, Luca Miccio <lucmiccio@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Marco Solieri <marco.solieri@xxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 06 May 2024 13:25:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.05.2024 18:55, Carlo Nonato wrote:
> From: Luca Miccio <lucmiccio@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> Signed-off-by: Marco Solieri <marco.solieri@xxxxxxxxxxxxxxx>
> Signed-off-by: Carlo Nonato <carlo.nonato@xxxxxxxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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