linux-kernel - Re: [arm64] kernel boot slowdown in v5.10.19 -> v5.10.42 update

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Message-ID: <7e43a7e9-f299-1d6d-8b61-425793abcc3e@linux.microsoft.com>
Date:   Fri, 28 Jan 2022 10:03:09 -0800
From:   Vijay Balakrishna <vijayb@...ux.microsoft.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Nicolas Saenz Julienne <nsaenz@...nel.org>
Subject: Re: [arm64] kernel boot slowdown in v5.10.19 -> v5.10.42 update



On 1/28/2022 4:06 AM, Catalin Marinas wrote:
> 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 >

Catalin,

Thanks for your reply.

CONFIG_RODATA_FULL_DEFAULT_ENABLED is not set in our config for boot 
time performance reasons.