[Bug 1888923] Re: Configured Memory access latency and bandwidth not taking effect

[Vishnu Dixit]

It indeed was a non NUMA machine

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Title:
  Configured Memory access latency and bandwidth not taking effect

Status in QEMU:
  Invalid

Bug description:
  I was trying to configure latencies and bandwidths between nodes in a
  NUMA emulation using QEMU 5.0.0.

  Host : Ubuntu 20.04 64 bit
  Guest : Ubuntu 18.04 64 bit

  The machine configured has 2 nodes. Each node has 2 CPUs and has been
  allocated 3GB of memory. The memory access latencies and bandwidths
  for a local access (i.e from initiator 0 to target 0, and from
  initiator 1 to target 1) are set as 40ns and 10GB/s respectively. The
  memory access latencies and bandwidths for a remote access (i.e from
  initiator 1 to target 0, and from initiator 0 to target 1) are set as
  80ns and 5GB/s respectively.

  The command line launch is as follows.

  sudo x86_64-softmmu/qemu-system-x86_64  \
  -machine hmat=on \
  -boot c \
  -enable-kvm \
  -m 6G,slots=2,maxmem=7G \
  -object memory-backend-ram,size=3G,id=m0 \
  -object memory-backend-ram,size=3G,id=m1 \
  -numa node,nodeid=0,memdev=m0 \
  -numa node,nodeid=1,memdev=m1 \
  -smp 4,sockets=4,maxcpus=4  \
  -numa cpu,node-id=0,socket-id=0 \
  -numa cpu,node-id=0,socket-id=1 \
  -numa cpu,node-id=1,socket-id=2 \
  -numa cpu,node-id=1,socket-id=3 \
  -numa dist,src=0,dst=1,val=20 \
  -net nic \
  -net user \
  -hda testing.img \
  -numa 
hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-latency,latency=40
 \
  -numa 
hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-bandwidth,bandwidth=10G
 \
  -numa 
hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-latency,latency=80
 \
  -numa 
hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-bandwidth,bandwidth=5G
 \
  -numa 
hmat-lb,initiator=1,target=0,hierarchy=memory,data-type=access-latency,latency=80
 \
  -numa 
hmat-lb,initiator=1,target=0,hierarchy=memory,data-type=access-bandwidth,bandwidth=5G
 \
  -numa 
hmat-lb,initiator=1,target=1,hierarchy=memory,data-type=access-latency,latency=40
 \
  -numa 
hmat-lb,initiator=1,target=1,hierarchy=memory,data-type=access-bandwidth,bandwidth=10G
 \

  Then the latencies and bandwidths between the nodes were tested using
  the Intel Memory Latency Checker v3.9
  (https://software.intel.com/content/www/us/en/develop/articles/intelr-
  memory-latency-checker.html). But the obtained results did not match
  the configuration. The following are the results obtained.

  Latency_matrix with idle latencies (in ns)

  Numa Node
  . .0. . .1.
  0 36.2 36.4
  1 34.9 35.4

  Bandwidth_matrix with memory bandwidths (in MB/s)

  Numa Node
  . . .0. . . .1. 
  0 15167.1 15308.9
  1 15226.0 15234.0

  A test was also conducted with the tool “lat_mem_rd” from lmbench to
  measure the memory read latencies. This also gave results which did
  not match the config.

  Any information on why the config latency and bandwidth values are not
  applied, would be appreciated.

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