Locality Group Observability on Solaris

Modern multi-socket servers exhibit NUMA characteristics that may hurt application performance if ignored. On a NUMA system (Non-uniform Memory Access), all memory is shared between/among processors. Each processor has access to its own memory - local memory - as well as memory that is local to another processor -- remote memory. However the memory access time (latency) depends on the memory location relative to the processor. A processor can access its local memory faster than the remote memory, and these varying memory latencies play a big role in application performance.

Solaris organizes the hardware resources -- CPU, memory and I/O devices -- into one or more logical groups based on their proximity to each other in such a way that all the hardware resources in a group are considered local to that group. These groups are referred as locality groups or NUMA nodes. In other words, a locality group (lgroup) is an abstraction that tells what hardware resources are near each other on a NUMA system. Each locality group has at least one processor and possibly some associated memory and/or IO devices. To minimize the impact of NUMA characteristics, Solaris considers the lgroup based physical topology when mapping threads and data to CPUs and memory.

Note that even though Solaris attempts to provide good performance out of the box, some applications may still suffer the impact of NUMA either due to misconfiguration of the hardware/software or some other reason. Engineered systems such as Oracle SuperCluster go to great lengths in setting up customer environments to minimize the impact of NUMA so applications perform as expected in a predictable manner. Still application developers and system/application administrators need to take NUMA factor into account while developing for and managing applications on large systems. Solaris provided tools and APIs can be used to observe, diagnose, control and even correct or fix the issues related to locality and latency. Rest of this post is about the tools that can be used to examine the locality of cores, memory and I/O devices.

Sample outputs are collected from a SPARC T4-4 server.

Locality Group Hierarchy

lgrpinfo prints information about the lgroup hierarchy and its contents. It is useful in understanding the context in which the OS is trying to optimize applications for locality, and also in figuring out which CPUs are closer, how much memory is near them, and the relative latencies between the CPUs and different memory blocks.

eg.,

# lgrpinfo -a

lgroup 0 (root):
        Children: 1-4
        CPUs: 0-255
        Memory: installed 1024G, allocated 75G, free 948G
        Lgroup resources: 1-4 (CPU); 1-4 (memory)
        Latency: 18
lgroup 1 (leaf):
        Children: none, Parent: 0
        CPUs: 0-63
        Memory: installed 256G, allocated 18G, free 238G
        Lgroup resources: 1 (CPU); 1 (memory)
        Load: 0.0227
        Latency: 12
lgroup 2 (leaf):
        Children: none, Parent: 0
        CPUs: 64-127
        Memory: installed 256G, allocated 15G, free 241G
        Lgroup resources: 2 (CPU); 2 (memory)
        Load: 0.000153
        Latency: 12
lgroup 3 (leaf):
        Children: none, Parent: 0
        CPUs: 128-191
        Memory: installed 256G, allocated 20G, free 236G
        Lgroup resources: 3 (CPU); 3 (memory)
        Load: 0.016
        Latency: 12
lgroup 4 (leaf):
        Children: none, Parent: 0
        CPUs: 192-255
        Memory: installed 256G, allocated 23G, free 233G
        Lgroup resources: 4 (CPU); 4 (memory)
        Load: 0.00824
        Latency: 12

Lgroup latencies:

------------------
  |  0  1  2  3  4
------------------
0 | 18 18 18 18 18
1 | 18 12 18 18 18
2 | 18 18 12 18 18
3 | 18 18 18 12 18
4 | 18 18 18 18 12
------------------

CPU Locality

lgrpinfo utility shown above already provides CPU locality in a clear manner. Here is another way to retrieve the association between CPU ids and lgroups.

# echo ::lgrp -p | mdb -k

   LGRPID  PSRSETID      LOAD      #CPU      CPUS
        1         0     17873        64      0-63
        2         0     17755        64      64-127
        3         0      2256        64      128-191
        4         0     18173        64      192-255

Memory Locality

lgrpinfo utility shown above shows the total memory that belongs to each of the locality groups. However, it doesn't show exactly what memory blocks belong to what locality groups. One of mdb's debugger command (dcmd) helps retrieve this information.

1. List memory blocks

# ldm list-devices -a memory

MEMORY
     PA                   SIZE            BOUND
     0xa00000             32M             _sys_
     0x2a00000            96M             _sys_
     0x8a00000            374M            _sys_
     0x20000000           1048064M        primary


2. Print the physical memory layout of the system

# echo ::syslayout | mdb -k

         STARTPA            ENDPA  SIZE  MG MN    STL    ETL
        20000000        200000000  7.5g   0  0      4     40
       200000000        400000000    8g   1  1    800    840
       400000000        600000000    8g   2  2   1000   1040
       600000000        800000000    8g   3  3   1800   1840
       800000000        a00000000    8g   0  0     40     80
       a00000000        c00000000    8g   1  1    840    880
       c00000000        e00000000    8g   2  2   1040   1080
       e00000000       1000000000    8g   3  3   1840   1880
      1000000000       1200000000    8g   0  0     80     c0
      1200000000       1400000000    8g   1  1    880    8c0
      1400000000       1600000000    8g   2  2   1080   10c0
      1600000000       1800000000    8g   3  3   1880   18c0
 ...
 ...

The values under MN column (memory node) can be treated as lgroup numbers after adding 1 to existing values. For example, a value of zero under MN translates to lgroup 1, 1 under MN translate to lgroup 2 and so on. Better yet, ::mnode debugger command lists out the mapping of mnodes to lgroups as shown below.

# echo ::mnode | mdb -k

           MNODE ID LGRP ASLEEP UTOTAL  UFREE UCACHE KTOTAL  KFREE KCACHE
     2075ad80000  0    1      -   249g   237g   114m   5.7g   714m      -
     2075ad802c0  1    2      -   240g   236g   288m    15g   4.8g      -
     2075ad80580  2    3      -   246g   234g   619m   9.6g   951m      -
     2075ad80840  3    4      -   247g   231g    24m     9g   897m      -

Unrelated notes:

• Main memory on T4-4 is interleaved across all memory banks with 8 GB interleave size -- meaning first 8 GB chunk excluding _sys_ blocks will be populated in lgroup 1 closer to processor #1, second 8 GB chunk in lgroup 2 closer to processor #2, third 8 GB chunk in lgroup 3 closer to processor #3, fourth 8 GB chunk in lgroup 4 closer to processor #4 and then the fifth 8 GB chunk again in lgroup 1 closer to processor #1 and so on. Memory is not interleaved on T5 and M6 systems (confirm by running the ::syslayout dcmd). Conceptually memory interleaving is similar to disk striping.

• Keep in mind that debugger commands (dcmd) are not committed - thus, there is no guarantee that they continue to work on future versions of Solaris. Some of these dcmds may not work on some of the existing versions of Solaris.

I/O Device Locality

-d option to lgrpinfo utility accepts a specified path to an I/O device and return the lgroup IDs closest to that device. Each I/O device on the system can be connected to one or more NUMA nodes - so, it is not uncommon to see more than one lgroup ID returned by lgrpinfo.

eg.,

# lgrpinfo -d /dev/dsk/c1t0d0
lgroup ID : 1

# dladm show-phys | grep 10000
net4              Ethernet             up         10000  full      ixgbe0

# lgrpinfo -d /dev/ixgbe0
lgroup ID : 1

# dladm show-phys | grep ibp0
net12             Infiniband           up         32000  unknown   ibp0

# lgrpinfo -d /dev/ibp0
lgroup IDs : 1-4

NUMA IO Groups

Debugger command ::numaio_group shows information about all NUMA I/O Groups.

# dladm show-phys | grep up
net0              Ethernet             up         1000   full      igb0
net12             Ethernet             up         10     full      usbecm2
net4              Ethernet             up         10000  full      ixgbe0

# echo ::numaio_group | mdb -k
            ADDR GROUP_NAME                     CONSTRAINT
    10050e1eba48 net4                  lgrp : 1
    10050e1ebbb0 net0                  lgrp : 1
    10050e1ebd18 usbecm2               lgrp : 1
    10050e1ebe80 scsi_hba_ngrp_mpt_sas1  lgrp : 4
    10050e1ebef8 scsi_hba_ngrp_mpt_sas0  lgrp : 1

Relying on prtconf is another way to find the NUMA IO locality for an IO device.

eg.,

# dladm show-phys | grep up | grep ixgbe
net4              Ethernet             up         10000  full      ixgbe0

== Find the device path for the network interface ==
# grep ixgbe /etc/path_to_inst | grep " 0 "
"/pci@400/pci@1/pci@0/pci@4/network@0" 0 "ixgbe"

== Find NUMA IO Lgroups ==
# prtconf -v /devices/pci@400/pci@1/pci@0/pci@4/network@0
 ...
    Hardware properties:
 ...
        name='numaio-lgrps' type=int items=1
            value=00000001
 ...

Process, Thread Locality

• -H of prstat command shows the home lgroup of active user processes and threads.

• -h of ps command can be used to examine the home lgroup of all user processes and threads. -H option can be used to list all processes that are in a certain locality group.
          [Related] Solaris assigns a thread to an lgroup when the thread is created. That lgroup is called the thread's home lgroup. Solaris runs the thread on the CPUs in the thread's home lgroup and allocates memory from that lgroup whenever possible.

• plgrp tool shows the placement of threads among locality groups. Same tool can be used to set the home locality group and lgroup affinities for one or more processes, threads, or LWPs.

• -L option of pmap command shows the lgroup that contains the physical memory backing some virtual memory.
          [Related] Breakdown of Oracle SGA into Solaris Locality Groups

• Memory placement among lgroups can possibly be achieved using pmadvise when the application is running or by using madvise() system call during development, which provides advice to the kernel's virtual memory manager. The OS will use this hint to determine how to allocate memory for the specified range. This mechanism is beneficial when the administrators and developers understand the target application's data access patterns.

  It is not possible to specify memory placement locality for OSM & ISM segments using pmadvise command or madvise() system call (DISM is an exception).

Examples:

# prstat -H

   PID USERNAME  SIZE   RSS STATE   PRI NICE      TIME  CPU LGRP PROCESS/NLWP
  1865 root      420M  414M sleep    59    0 447:51:13 0.1%    2 java/108
  3659 oracle   1428M 1413M sleep    38    0  68:39:28 0.0%    4 oracle/1
  1814 oracle    155M  110M sleep    59    0  70:45:17 0.0%    4 gipcd.bin/9
     8 root        0K    0K sleep    60    -  70:52:21 0.0%    0 vmtasks/257
  3765 root      447M  413M sleep    59    0  29:24:20 0.0%    3 crsd.bin/43
  3949 oracle    505M  456M sleep    59    0   0:59:42 0.0%    2 java/124
 10825 oracle   1097M 1074M sleep    59    0  18:13:27 0.0%    3 oracle/1
  3941 root      210M  184M sleep    59    0  20:03:37 0.0%    4 orarootagent.bi/14
  3743 root      119M   98M sleep   110    -  24:53:29 0.0%    1 osysmond.bin/13
  3324 oracle    266M  225M sleep   110    -  19:52:31 0.0%    4 ocssd.bin/34
  1585 oracle    122M   91M sleep    59    0  18:06:34 0.0%    3 evmd.bin/10
  3918 oracle    168M  144M sleep    58    0  14:35:31 0.0%    1 oraagent.bin/28
  3427 root      112M   80M sleep    59    0  12:34:28 0.0%    4 octssd.bin/12
  3635 oracle   1425M 1406M sleep   101    -  13:55:31 0.0%    4 oracle/1
  1951 root      183M  161M sleep    59    0   9:26:51 0.0%    4 orarootagent.bi/21
Total: 251 processes, 2414 lwps, load averages: 1.37, 1.46, 1.47

== Locality group 2 is the home lgroup of the java process with pid 1865 == 

# plgrp 1865

     PID/LWPID    HOME
    1865/1        2
    1865/2        2
 ...
 ...
    1865/22       4
    1865/23       4
 ...
 ...
    1865/41       1
    1865/42       1
 ...
 ...
    1865/60       3
    1865/61       3
 ...
 ...

# plgrp 1865 | awk '{print $2}' | grep 2 | wc -l
      30

# plgrp 1865 | awk '{print $2}' | grep 1 | wc -l
      25

# plgrp 1865 | awk '{print $2}' | grep 3 | wc -l
      25

# plgrp 1865 | awk '{print $2}' | grep 4 | wc -l
      28


== Let's reset the home lgroup of the java process id 1865 to 4 ==


# plgrp -H 4 1865
     PID/LWPID    HOME
    1865/1        2 => 4
    1865/2        2 => 4
    1865/3        2 => 4
    1865/4        2 => 4
 ...
 ...
    1865/184      1 => 4
    1865/188      4 => 4

# plgrp 1865 | awk '{print $2}' | egrep "1|2|3" | wc -l
       0

# plgrp 1865 | awk '{print $2}' | grep 4 | wc -l
     108

# prstat -H -p 1865

   PID USERNAME  SIZE   RSS STATE   PRI NICE      TIME  CPU LGRP PROCESS/NLWP
  1865 root      420M  414M sleep    59    0 447:57:30 0.1%    4 java/108

== List the home lgroup of all processes ==

# ps -aeH
  PID LGRP TTY         TIME CMD
    0    0 ?           0:11 sched
    5    0 ?           4:47 zpool-rp
    1    4 ?          21:04 init
    8    0 ?        4253:54 vmtasks
   75    4 ?           0:13 ipmgmtd
   11    3 ?           3:09 svc.star
   13    4 ?           2:45 svc.conf
 3322    1 ?         301:51 cssdagen
 ...
11155    3 ?           0:52 oracle
13091    4 ?           0:00 sshd
13124    3 pts/5       0:00 bash
24703    4 pts/8       0:00 bash
12812    2 pts/3       0:00 bash
 ...

== Find out the lgroups which shared memory segments are allocated from ==

# pmap -Ls 24513 | egrep "Lgrp|256M|2G"

         Address       Bytes Pgsz Mode   Lgrp Mapped File
0000000400000000   33554432K   2G rwxs-    1   [ osm shmid=0x78000047 ]
0000000C00000000     262144K 256M rwxs-    3   [ osm shmid=0x78000048 ]
0000000C10000000     524288K 256M rwxs-    2   [ osm shmid=0x78000048 ]
0000000C30000000     262144K 256M rwxs-    3   [ osm shmid=0x78000048 ]
0000000C40000000     524288K 256M rwxs-    1   [ osm shmid=0x78000048 ]
0000000C60000000     262144K 256M rwxs-    2   [ osm shmid=0x78000048 ]

== Apply MADV_ACCESS_LWP policy advice to a segment at a specific address ==

# pmap -Ls 1865 | grep anon

00000007DAC00000      20480K   4M rw---    4   [ anon ]
00000007DC000000       4096K    - rw---    -   [ anon ]
00000007DFC00000      90112K   4M rw---    4   [ anon ]
00000007F5400000     110592K   4M rw---    4   [ anon ]

# pmadvise -o 7F5400000=access_lwp 1865

# pmap -Ls 1865 | grep anon
00000007DAC00000      20480K   4M rw---    4   [ anon ]
00000007DC000000       4096K    - rw---    -   [ anon ]
00000007DFC00000      90112K   4M rw---    4   [ anon ]
00000007F5400000      73728K   4M rw---    4   [ anon ]
00000007F9C00000      28672K    - rw---    -   [ anon ]
00000007FB800000       8192K   4M rw---    4   [ anon ]

SEE ALSO:

• - Man pages of lgrpinfo(1), plgrp(1), pmap(1), prstat(1M), ps(1), pmadvise(1), madvise(3C), madv.so.1(1), mdb(1)
• - Web search keywords: NUMA, cc-NUMA, locality group, lgroup, lgrp, Memory Placement Optimization, MPO