On Mon, Jan 24, 2022 at 03:03:48PM -0800, Vijay Balakrishna wrote:
We noticed 150ms kernel boot slowdown back in June, 2021, when moving from
v5.10.19 to v5.10.42. This on a 8GB SoC. Only recently we investigated
this issue and found the regression is introduced by a change in map_mem()
(paging_init() -> map_mem() -> __map_memblock(), in particular "map all the
memory banks" for loop) by patch
2687275a5843d1089687f08fc64eb3f3b026a169
arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required
above is a follow up to
0a30c53573b07d5561457e41fb0ab046cd857da5
arm64: mm: Move reserve_crashkernel() into mem_init())
which deferred crashkernel reservation into mem_init().
The ~150ms slowdown disappears on booting without "crashkernel=.." on kernel
command-line.
Is CONFIG_RODATA_FULL_DEFAULT_ENABLED set in your config file? It may
cause the same slowdown. I suspect it's because we end up mapping the
RAM at the page granularity so more loops and slightly higher TLB
pressure. Not sure we can do much about >