56 lines
2.4 KiB
ReStructuredText
56 lines
2.4 KiB
ReStructuredText
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===============================
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Numa policy hit/miss statistics
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===============================
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/sys/devices/system/node/node*/numastat
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All units are pages. Hugepages have separate counters.
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The numa_hit, numa_miss and numa_foreign counters reflect how well processes
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are able to allocate memory from nodes they prefer. If they succeed, numa_hit
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is incremented on the preferred node, otherwise numa_foreign is incremented on
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the preferred node and numa_miss on the node where allocation succeeded.
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Usually preferred node is the one local to the CPU where the process executes,
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but restrictions such as mempolicies can change that, so there are also two
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counters based on CPU local node. local_node is similar to numa_hit and is
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incremented on allocation from a node by CPU on the same node. other_node is
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similar to numa_miss and is incremented on the node where allocation succeeds
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from a CPU from a different node. Note there is no counter analogical to
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numa_foreign.
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In more detail:
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=============== ============================================================
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numa_hit A process wanted to allocate memory from this node,
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and succeeded.
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numa_miss A process wanted to allocate memory from another node,
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but ended up with memory from this node.
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numa_foreign A process wanted to allocate on this node,
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but ended up with memory from another node.
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local_node A process ran on this node's CPU,
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and got memory from this node.
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other_node A process ran on a different node's CPU
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and got memory from this node.
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interleave_hit Interleaving wanted to allocate from this node
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and succeeded.
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=============== ============================================================
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For easier reading you can use the numastat utility from the numactl package
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(http://oss.sgi.com/projects/libnuma/). Note that it only works
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well right now on machines with a small number of CPUs.
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Note that on systems with memoryless nodes (where a node has CPUs but no
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memory) the numa_hit, numa_miss and numa_foreign statistics can be skewed
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heavily. In the current kernel implementation, if a process prefers a
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memoryless node (i.e. because it is running on one of its local CPU), the
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implementation actually treats one of the nearest nodes with memory as the
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preferred node. As a result, such allocation will not increase the numa_foreign
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counter on the memoryless node, and will skew the numa_hit, numa_miss and
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numa_foreign statistics of the nearest node.
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