kvm/powerpc: memcached benchmark

[Yu Zhao <yuzhao@google.com>]

TLDR
====
Memcached achieved 10% more operations per second (in ~4 hours) after this patchset [1].

Hardware
========
HOST $ lscpu
Architecture:          ppc64le
  Byte Order:          Little Endian
CPU(s):                184
  On-line CPU(s) list: 0-183
Model name:            POWER9 (raw), altivec supported
  Model:               2.2 (pvr 004e 1202)
  Thread(s) per core:  4
  Core(s) per socket:  23
  Socket(s):           2
  CPU max MHz:         3000.0000
  CPU min MHz:         2300.0000
Caches (sum of all):
  L1d:                 1.4 MiB (46 instances)
  L1i:                 1.4 MiB (46 instances)
  L2:                  12 MiB (24 instances)
  L3:                  240 MiB (24 instances)
NUMA:
  NUMA node(s):        2
  NUMA node0 CPU(s):   0-91
  NUMA node1 CPU(s):   92-183
Vulnerabilities:
  Itlb multihit:       Not affected
  L1tf:                Mitigation; RFI Flush, L1D private per thread
  Mds:                 Not affected
  Meltdown:            Mitigation; RFI Flush, L1D private per thread
  Mmio stale data:     Not affected
  Retbleed:            Not affected
  Spec store bypass:   Mitigation; Kernel entry/exit barrier (eieio)
  Spectre v1:          Mitigation; __user pointer sanitization, ori31 speculation barrier enabled
  Spectre v2:          Mitigation; Indirect branch serialisation (kernel only), Indirect branch cache disabled, Software link stack flush
  Srbds:               Not affected
  Tsx async abort:     Not affected

HOST $ numactl -H
available: 2 nodes (0-1)
node 0 cpus: 0-91
node 0 size: 261659 MB
node 0 free: 259152 MB
node 1 cpus: 92-183
node 1 size: 261713 MB
node 1 free: 261076 MB
node distances:
node   0   1
  0:  10  40
  1:  40  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 LTS"

HOST $ uname -a
Linux ppc 6.3.0 #1 SMP Sun Jun  4 18:26:37 UTC 2023 ppc64le ppc64le ppc64le GNU/Linux

HOST $ cat /proc/swaps
Filename          Type         Size         Used    Priority
/dev/nvme0n1p2    partition	    466838272    0       -2

HOST $ cat /sys/kernel/mm/lru_gen/enabled
0x0009

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]

HOST $ qemu-system-ppc64 --version
QEMU emulator version 6.2.0 (Debian 1:6.2+dfsg-2ubuntu6.6)
Copyright (c) 2003-2021 Fabrice Bellard and the QEMU Project developers

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

GUEST $ cat /etc/memcached.conf
...
-t 92
-m 262144
-B binary
-s /var/run/memcached/memcached.sock
-a 0766

GUEST $ memtier_benchmark -v
memtier_benchmark 1.4.0
Copyright (C) 2011-2022 Redis Ltd.
This is free software.  You may redistribute copies of it under the terms of
the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.

Procedure
=========
HOST $ sudo numactl -N 0 -m 0 qemu-system-ppc64 \
    -M pseries,accel=kvm,kvm-type=HV -cpu host -smp 92 -m 270g
    -nographic -nic user \
    -drive if=virtio,format=raw,file=/dev/nvme0n1p1

GUEST $ memtier_benchmark -S /var/run/memcached/memcached.sock \
    -P memcache_binary -c 1 -t 92 --pipeline 1 --ratio 1:0 \
    --key-minimum=1 --key-maximum=120000000 --key-pattern=P:P \
    -n allkeys -d 2000

GUEST $ memtier_benchmark -S /var/run/memcached/memcached.sock \
    -P memcache_binary -c 1 -t 92 --pipeline 1 --ratio 0:1 \
    --key-minimum=1 --key-maximum=120000000 --key-pattern=R:R \
    -n allkeys --randomize --distinct-client-seed

Results
=======
                Before [1]    After        Change
-------------------------------------------------
Ops/sec         721586.10     800210.12    +10%
Avg. Latency    0.12546       0.11260      -10%
p50 Latency     0.08700       0.08700      N/C
p99 Latency     0.28700       0.24700      -13%

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/