CONFIG_TRACER_SNAPSHOT_PER_CPU_SWAP: Allow snapshot to swap per CPU

General informations

The Linux kernel configuration item CONFIG_TRACER_SNAPSHOT_PER_CPU_SWAP:

• prompt: Allow snapshot to swap per CPU
• type: bool
• depends on: CONFIG_TRACER_SNAPSHOT
• defined in kernel/trace/Kconfig
• found in Linux kernels: 3.10–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

Allow doing a snapshot of a single CPU buffer instead of a full swap (all buffers). If this is set, then the following is allowed:

echo 1 > /sys/kernel/tracing/per_cpu/cpu2/snapshot

After which, only the tracing buffer for CPU 2 was swapped with the main tracing buffer, and the other CPU buffers remain the same.

When this is enabled, this adds a little more overhead to the trace recording, as it needs to add some checks to synchronize recording with swaps. But this does not affect the performance of the overall system. This is enabled by default when the preempt or irq latency tracers are enabled, as those need to swap as well and already adds the overhead (plus a lot more).

Hardware

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The data is retrived from:

• Linux kernel
• Linux Kernel Driver DataBase (LKDDb)

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