Use recommended clocksources #1328
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cartermckinnon
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Jun 15, 2023
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| cat << EOF | sudo tee -a /etc/chrony.conf | ||
| # This directive enables kernel synchronisation (every 11 minutes) of the | ||
| # real-time clock. Note that it can’t be used along with the 'rtcfile' directive. | ||
| rtcsync | ||
| EOF |
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I verified that this is already present in /etc/chrony.conf in the latest AL2 minimal AMI. We should not configure chrony here to avoid diverging from the defaults provided by AL2.
cartermckinnon
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Jun 15, 2023
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| # If current clocksource is xen, switch to tsc | ||
| if grep --quiet xen /sys/devices/system/clocksource/clocksource0/current_clocksource \ | ||
| && grep --quiet tsc /sys/devices/system/clocksource/clocksource0/available_clocksource; then | ||
| echo "tsc" | sudo tee /sys/devices/system/clocksource/clocksource0/current_clocksource | ||
| else | ||
| echo "tsc as a clock source is not applicable, skipping." | ||
| fi |
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This only sets the current clocksource, which has no effect after a reboot.
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cartermckinnon
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Jun 16, 2023
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| # use the tsc clocksource by default | ||
| # https://repost.aws/knowledge-center/manage-ec2-linux-clock-source | ||
| sudo grubby \ | ||
| --update-kernel=ALL \ | ||
| --args="clocksource=tsc tsc=reliable" | ||
|
|
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This isn't strictly necessary with the configure-clocksource unit in place, but the tsc=reliable flag is still worth setting, and we might as well configure a default here too.
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Issue #, if available:
Fixes #249
Description of changes:
The
tscclocksource is the recommended default for instances on the Xen hypervisor, as it's significantly more performant than thexenclocksource (there's an interesting case study from Netflix).A previous attempt (in #272) to swap
xenfortschad no effect; only the current clocksource was changed, not the default. The setting was applied during the AMI build process and had no effect after a reboot.EC2 recommends:
tscxenwas used by default.kvm-clocktscwas used by default.arch_sys_counterclocksourceset on the kernel command-line is ignored.By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.
Testing Done
make 1.27).m6i.large(Nitro):kvm-clockused as expected.r7g.medium(Graviton3):arch_sys_counterused as expected.arm64variant for this (make 1.27 arch=arm64).m4.large(Xen):tscused as expected.