43 lines
1.2 KiB
ReStructuredText
43 lines
1.2 KiB
ReStructuredText
==========================
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Map CPUs to Scylla Shards
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==========================
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Due to its thread-per-core architecture, many things within Scylla can be better understood when you look at it on a per-CPU basis. There are Linux tools such as ``top`` and ``perf`` that can give information about what is happening within a CPU, given a CPU number.
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A common mistake users make is to assume that there is a direct and predictable relationship between the Scylla Shard ID and the CPU ID, which is not true.
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Starting in version 3.0, Scylla ships with a script to let users know about the mapping between CPUs and Scylla Shards. For users of older versions, a copy of the script can be downloaded from the `Seastar git tree <https://raw.githubusercontent.com/scylladb/seastar/master/scripts/seastar-cpu-map.sh>`_.
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Examples of usage
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------------------
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To list the mapping of a specific shard:
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.. code-block:: bash
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seastar-cpu-map.sh -n scylla -s 0
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Output:
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.. code-block:: console
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:class: hide-copy-button
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shard: 0, cpu: 1
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To list the mapping of all shards:
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.. code-block:: bash
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seastar-cpu-map.sh -n scylla
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Output:
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.. code-block:: console
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:class: hide-copy-button
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shard: 0, cpu: 1
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shard: 1, cpu: 2
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shard: 3, cpu: 4
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shard: 2, cpu: 3
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