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setting GRUB_CMDLINE_LINUX, example usage of perf c2c #420

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Oct 2, 2024
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setting GRUB_CMDLINE_LINUX, example usage of perf c2c #420

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8 changes: 7 additions & 1 deletion perfrunbook/debug_hw_perf.md
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Expand Up @@ -213,7 +213,8 @@ On Ubuntu to enable SPE requires four extra steps
# Install the arm_spe_pmu.ko module
sudo apt install linux-modules-extra-$(uname -r)

# Add kpti=off to the kernel boot command line
# Add kpti=off to the kernel boot command line: GRUB_CMDLINE_LINUX in /etc/default/grub, to set it for all the installed kernels.
# Note, the options passed to GRUB_CMDLINE_LINUX_DEFAULT will only propagate to the default kernel and not to all the installed kernels.
# Reboot instance

sudo modprobe arm_spe_pmu
Expand All @@ -230,6 +231,11 @@ the samples directly, you can use the [Arm SPE Parser](https://gitlab.arm.com/te

Be aware that SPE produces a large of volume of data (many GBs) if the sampling period is low and you collect the data over a long time.

### Capturing cache coherence issues
The `perf c2c` command can be used to analyze cache coherence issues and false sharing in multi-core systems. It needs SPE PMU available on Graviton metal instances.

`perf c2c record ./application`

### Capturing Coherent Mesh Network (CMN) hardware events on Graviton metal instances

On Graviton the CMN connects the CPUs to each other, to the memory controller, the I/O subsystem and provides the System Level Cache.
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