defer squashfs mounts #2276
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defer squashfs mounts #2276
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Mounting `/usr/share/licenses` and `/usr/src/kernels` can add up to one second of delay before reaching `local-fs.target`. It's not necessary to read software licenses or build out-of-tree kernel modules at this stage in the boot process. Moving the mounts after `local-fs.target` doesn't eliminate the delay, but does allow the system to do other useful work in parallel, like acquiring DHCP leases and applying settings. Signed-off-by: Ben Cressey <[email protected]>
arnaldo2792
approved these changes
Jul 18, 2022
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Issue number:
N/A
Description of changes:
Mounting
/usr/share/licensesand/usr/src/kernelscan add up to one second of delay before reachinglocal-fs.target.It's not necessary to read software licenses or build out-of-tree kernel modules at this stage in the boot process. Moving the mounts after
local-fs.targetdoesn't eliminate the delay, but does allow the system to do other useful work in parallel, like acquiring DHCP leases and applying settings.Testing done:
I verified that
link-kernel-modules.serviceandload-kernel-modulesrun correctly on theaws-k8s-1.22-nvidiavariant.It's difficult to quantify the actual benefit of this since it can vary widely, and depends on other factors like the amount of console logging and whether the wrong kernel thread gets "stuck" flushing to the console when these messages are printed:
Instead I'll just point to the actual mount unit times:
These are consistently the two slowest mounts, and intuitively it is preferable to deal with slow mounts later in boot if possible, to avoid unlucky sequences where the system stalls for 300 ms before reaching
local-fs.target.Terms of contribution:
By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.