kvm/x86: multichase benchmark

[Yu Zhao <yuzhao@google.com>]

TLDR
====
Multichase in 64 microVMs achieved 6% more total samples (in ~4 hours) after this patchset [1].

Hardware
========
HOST $ lscpu
Architecture:            x86_64
  CPU op-mode(s):        32-bit, 64-bit
  Address sizes:         43 bits physical, 48 bits virtual
  Byte Order:            Little Endian
CPU(s):                  128
  On-line CPU(s) list:   0-127
Vendor ID:               AuthenticAMD
  Model name:            AMD Ryzen Threadripper PRO 3995WX 64-Cores
    CPU family:          23
    Model:               49
    Thread(s) per core:  2
    Core(s) per socket:  64
    Socket(s):           1
    Stepping:            0
    Frequency boost:     disabled
    CPU max MHz:         4308.3979
    CPU min MHz:         2200.0000
    BogoMIPS:            5390.20
    Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2
                         ...
Virtualization features:
  Virtualization:        AMD-V
Caches (sum of all):
  L1d:                   2 MiB (64 instances)
  L1i:                   2 MiB (64 instances)
  L2:                    32 MiB (64 instances)
  L3:                    256 MiB (16 instances)
NUMA:
  NUMA node(s):          1
  NUMA node0 CPU(s):     0-127
Vulnerabilities:
  Itlb multihit:         Not affected
  L1tf:                  Not affected
  Mds:                   Not affected
  Meltdown:              Not affected
  Mmio stale data:       Not affected
  Retbleed:              Mitigation; untrained return thunk; SMT enabled with STIBP protection
  Spec store bypass:     Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:            Mitigation; usercopy/swapgs barriers and __user pointer sanitization
  Spectre v2:            Mitigation; Retpolines, IBPB conditional, STIBP always-on, RSB filling, PBRSB-eIBRS Not affected
  Srbds:                 Not affected
  Tsx async abort:       Not affected

HOST $ numactl -H
available: 1 nodes (0)
node 0 cpus: 0-127
node 0 size: 257542 MB
node 0 free: 224855 MB
node distances:
node   0
  0:  10

HOST $ cat /sys/class/nvme/nvme0/model
INTEL SSDPF21Q800GB

HOST $ cat /sys/class/nvme/nvme0/numa_node
0

Software
========
HOST $ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04.1 LTS"

HOST $ uname -a
Linux x86 6.4.0-rc5+ #1 SMP PREEMPT_DYNAMIC Wed Jun  7 22:17:47 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

HOST $ cat /proc/swaps
Filename          Type         Size         Used    Priority
/dev/nvme0n1p2    partition    466838356    0       -2

HOST $ cat /sys/kernel/mm/lru_gen/enabled
0x000f

HOST $ cat /sys/kernel/mm/transparent_hugepage/enabled
always madvise [never]

HOST $ cat /sys/kernel/mm/transparent_hugepage/defrag
always defer defer+madvise madvise [never]

Procedure
=========
HOST $ git clone https://github.com/google/multichase

HOST $ <Build multichase>
HOST $ <Unpack /boot/initrd.img into ./initrd/>

HOST $ cp multichase/multichase ./initrd/bin/
HOST $ sed -i \
    "/^maybe_break top$/i multichase -t 2 -m 4g -n 28800; poweroff" \
    ./initrd/init

HOST $ <Pack ./initrd/ into ./initrd.img>

HOST $ cat run_microvms.sh
memcgs=64

run() {
    path=/sys/fs/cgroup/memcg$1

    mkdir $path
    echo $BASHPID >$path/cgroup.procs

    qemu-system-x86_64 -M microvm,accel=kvm -cpu host -smp 2 -m 6g \
        -nographic -kernel /boot/vmlinuz -initrd ./initrd.img \
        -append "console=ttyS0 loglevel=0"
}

for ((memcg = 0; memcg < $memcgs; memcg++)); do
    run $memcg &
done

wait

Results
=======
                 Before [1]    After    Change
----------------------------------------------
Total samples    6824          7237     +6%

Notes
=====
[1] "mm: rmap: Don't flush TLB after checking PTE young for page
    reference" was included so that the comparison is apples to
    Apples.
    https://lore.kernel.org/r/20220706112041.3831-1-21cnbao@gmail.com/