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ACPI RQSC Proof of Concept

ACPI RQSC Proof of Concept

Owned by Drew Fustini
Last updated: Mar 30, 2025
4 min read

This page describes the software Proof of Concept (PoC) for the ACPI RQSC table which describes QoS controllers in the system that implement the Capacity and Bandwidth QoS Register Interface (CBQRI).

This PoC builds upon the original CBQRI PoC. Linux now supports CBQRI controller information passed through Device Tree or ACPI. The choice depends on how Qemu is invoked - see below for details.

Resources

ACPI RQSC table spec

https://github.com/riscv-non-isa/riscv-rqsc/tree/main/src

The Capacity and Bandwidth QoS controllers in a system are described by the ACPI RQSC table. The actual register interface is specified in the RISC-V Capacity and Bandwidth Controller QoS Register Interface specification cite:[CBQRI].

The RQSC table describes the properties of the QoS controllers in the system. The table also describes the topological arrangement of the QoS controllers and resources in the system. The topology is expressed in terms of the location of the resources within the system and the relation between teh QoS Controller and the resource it manages.

RVI PRS meeting

RQSC slides from RVI Platform Runtime Services (PRS) TG meeting on March 27, 2025.

Linux

Qemu

  • Repo: GitHub - tt-fustini/qemu

  • Branch: riscv-cbqri-rqsc-pptt

  • Build and run: ./build.sh && ./run-acpi.sh

    • TODO: add note about dependencies to build Qemu and EDK2

run-acpi.sh

#!/bin/bash export LX=$HOME/dev/linux export BR=$HOME/dev/images export EDK=$HOME/dev/edk2 build/qemu-system-riscv64 \ -M virt,pflash0=pflash0,pflash1=pflash1,aia=aplic-imsic \ -nographic \ -m 1G \ -smp cpus=8,sockets=1,clusters=2,cores=4,threads=1 \ -serial mon:stdio \ -kernel ${LX}/arch/riscv/boot/Image \ -append "root=/dev/vda ro loglevel=8 ro console=ttyS0 rootwait earlycon=uart8250,mmio,0x10000000 acpi.debug_layer=0xffffffff acpi.debug_level=0xffffffff" \ -blockdev node-name=pflash0,driver=file,read-only=on,filename=$EDK/RISCV_VIRT_CODE.fd \ -blockdev node-name=pflash1,driver=file,filename=$EDK/RISCV_VIRT_VARS.fd \ -drive if=none,file=${BR}/rootfs.ext2,format=raw,id=hd0 \ -device virtio-blk-device,drive=hd0 \ -device qemu-xhci \ -device usb-kbd \ -device virtio-net-pci,netdev=net0 \ -netdev user,id=net0 \ -device riscv.cbqri.capacity,max_mcids=256,max_rcids=64,ncblks=12,alloc_op_flush_rcid=false,mon_op_config_event=false,mon_op_read_counter=false,mon_evt_id_none=false,mon_evt_id_occupancy=false,mmio_base=0x04820000 \ -device riscv.cbqri.capacity,max_mcids=256,max_rcids=64,ncblks=12,alloc_op_flush_rcid=false,mon_op_config_event=false,mon_op_read_counter=false,mon_evt_id_none=false,mon_evt_id_occupancy=false,mmio_base=0x04821000 \ -device riscv.cbqri.capacity,max_mcids=256,max_rcids=64,ncblks=16,mmio_base=0x0482B000 \ -device riscv.cbqri.bandwidth,max_mcids=256,max_rcids=64,nbwblks=1024,mrbwb=819,mmio_base=0x04828000 \ -device riscv.cbqri.bandwidth,max_mcids=256,max_rcids=64,nbwblks=1024,mrbwb=819,mmio_base=0x04829000 \ -device riscv.cbqri.bandwidth,max_mcids=256,max_rcids=64,nbwblks=1024,mrbwb=819,mmio_base=0x0482a000 \ #-numa node,cpus=0-3,nodeid=0,mem=512M -numa node,cpus=4-7,nodeid=1,mem=512M \

PPTT table in Qemu

RQSC table in Qemu

Cache ID

Qemu uses the CBQRI controller's mmio_base address as the Cache ID in both the PPTT and RQSC tables for cache controllers. A real platform would probably do it differently but this is a simple way to ensure the Cache ID is unique.

The Linux PPTT driver is now able to populate the cache information for each cpu.
Example of cpu0 (cluster 0) and cpu4 (cluster 1). They have different instances of the L2 cache controller (note: sysfs prints the Cache ID in decimal).

for i in `find /sys/devices/system/cpu/cpu0/cache/index* -type f | grep -E '/(type|size|id|level)'`; do echo "$i: `cat $i`"; done /sys/devices/system/cpu/cpu0/cache/index0/id: 29 /sys/devices/system/cpu/cpu0/cache/index0/type: Data /sys/devices/system/cpu/cpu0/cache/index0/size: 64K /sys/devices/system/cpu/cpu0/cache/index0/level: 1 /sys/devices/system/cpu/cpu0/cache/index1/id: 30 /sys/devices/system/cpu/cpu0/cache/index1/type: Instruction /sys/devices/system/cpu/cpu0/cache/index1/size: 64K /sys/devices/system/cpu/cpu0/cache/index1/level: 1 /sys/devices/system/cpu/cpu0/cache/index2/id: 75632640 /sys/devices/system/cpu/cpu0/cache/index2/type: Unified /sys/devices/system/cpu/cpu0/cache/index2/size: 750K /sys/devices/system/cpu/cpu0/cache/index2/level: 2 /sys/devices/system/cpu/cpu0/cache/index3/id: 75673600 /sys/devices/system/cpu/cpu0/cache/index3/type: Unified /sys/devices/system/cpu/cpu0/cache/index3/size: 3072K /sys/devices/system/cpu/cpu0/cache/index3/level: 3 # for i in `find /sys/devices/system/cpu/cpu4/cache/index* -type f | grep -E '/(type|size|id|level)'`; do echo "$i: `cat $i`"; done /sys/devices/system/cpu/cpu4/cache/index0/id: 29 /sys/devices/system/cpu/cpu4/cache/index0/type: Data /sys/devices/system/cpu/cpu4/cache/index0/size: 64K /sys/devices/system/cpu/cpu4/cache/index0/level: 1 /sys/devices/system/cpu/cpu4/cache/index1/id: 30 /sys/devices/system/cpu/cpu4/cache/index1/type: Instruction /sys/devices/system/cpu/cpu4/cache/index1/size: 64K /sys/devices/system/cpu/cpu4/cache/index1/level: 1 /sys/devices/system/cpu/cpu4/cache/index2/id: 75628544 /sys/devices/system/cpu/cpu4/cache/index2/type: Unified /sys/devices/system/cpu/cpu4/cache/index2/size: 750K /sys/devices/system/cpu/cpu4/cache/index2/level: 2 /sys/devices/system/cpu/cpu4/cache/index3/id: 75673600 /sys/devices/system/cpu/cpu4/cache/index3/type: Unified /sys/devices/system/cpu/cpu4/cache/index3/size: 3072K /sys/devices/system/cpu/cpu4/cache/index3/level: 3

resctrl demo

The full resctrl user interface is documented in the kernel

Example commands to mount and modify the schemata:

mount -t resctrl resctrl /sys/fs/resctrl ls -la /sys/fs/resctrl/ cd /sys/fs/resctrl/ cat /sys/fs/resctrl/schemata echo 'L2:4=ff0' > /sys/fs/resctrl/schemata cat /sys/fs/resctrl/schemata

Running in Qemu:

# mount -t resctrl resctrl /sys/fs/resctrl # cd /sys/fs/resctrl/ # cat /sys/fs/resctrl/schemata MB:0=0;1=0;2=0 L2:4=0;5=0 L3:3=0 # echo 'L2:4=ff0' > /sys/fs/resctrl/schemata # echo 'L2:5=fff' > /sys/fs/resctrl/schemata # echo 'L2:5=0ff' > /sys/fs/resctrl/schemata # cat /sys/fs/resctrl/schemata MB:0=0;1=0;2=0 L2:4=ff0;5=ff L3:3=0 # echo 'L3:3=fff' > /sys/fs/resctrl/schemata # echo 'L3:3=ff0' > /sys/fs/resctrl/schemata # cat /sys/fs/resctrl/schemata MB:0=0;1=0;2=0 L2:4=ff0;5=ff L3:3=ff0 # mkdir p1 # cd p1 # echo $$ > tasks # cat schemata MB:0=100;1=100;2=100 L2:4=fff;5=fff L3:3=ffff # cat ../schemata MB:0=0;1=0;2=0 L2:4=ff0;5=ff L3:3=ff0

Boot log

 

pdp7@thelio:~/dev/qemu$ ./build.sh && ./run-acpi.sh # mount -t resctrl resctrl /sys/fs/resctrl # cd /sys/fs/resctrl/ # ls -la total 0 dr-xr-xr-x 5 root root 0 Jan 1 00:06 . drwxr-xr-x 9 root root 0 Jan 1 00:06 .. -rw-r--r-- 1 root root 0 Jan 1 00:06 cpus -rw-r--r-- 1 root root 0 Jan 1 00:06 cpus_list dr-xr-xr-x 6 root root 0 Jan 1 00:06 info -rw-r--r-- 1 root root 0 Jan 1 00:06 mode dr-xr-xr-x 2 root root 0 Jan 1 00:06 mon_data dr-xr-xr-x 2 root root 0 Jan 1 00:06 mon_groups -rw-r--r-- 1 root root 0 Jan 1 00:06 schemata -r--r--r-- 1 root root 0 Jan 1 00:06 size -rw-r--r-- 1 root root 0 Jan 1 00:06 tasks # cat /sys/fs/resctrl/schemata MB:0=0;1=0;2=0 L2:4=0;5=0 L3:3=0 # echo 'L2:4=ff0' > /sys/fs/resctrl/schemata # echo 'L2:5=fff' > /sys/fs/resctrl/schemata # echo 'L2:5=0ff' > /sys/fs/resctrl/schemata # cat /sys/fs/resctrl/schemata MB:0=0;1=0;2=0 L2:4=ff0;5=ff L3:3=0 # echo 'L3:3=fff' > /sys/fs/resctrl/schemata # echo 'L3:3=ff0' > /sys/fs/resctrl/schemata # cat /sys/fs/resctrl/schemata MB:0=0;1=0;2=0 L2:4=ff0;5=ff L3:3=ff0 # mkdir p1 # cd p1 # echo $$ > tasks # ls -la total 0 drwxr-xr-x 4 root root 0 Jan 1 00:07 . dr-xr-xr-x 6 root root 0 Jan 1 00:06 .. -rw-r--r-- 1 root root 0 Jan 1 00:07 cpus -rw-r--r-- 1 root root 0 Jan 1 00:07 cpus_list -rw-r--r-- 1 root root 0 Jan 1 00:07 mode drwxr-xr-x 2 root root 0 Jan 1 00:07 mon_data drwxr-xr-x 2 root root 0 Jan 1 00:07 mon_groups -rw-r--r-- 1 root root 0 Jan 1 00:07 schemata -r--r--r-- 1 root root 0 Jan 1 00:07 size -rw-r--r-- 1 root root 0 Jan 1 00:07 tasks # pwd /sys/fs/resctrl/p1 # cat schemata MB:0=100;1=100;2=100 L2:4=fff;5=fff L3:3=ffff # cat ../schemata MB:0=0;1=0;2=0 L2:4=ff0;5=ff L3:3=ff0 #

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