linux-kernel - Re: [RFC PATCH 0/4] Speed booting by sorting ORC unwind tables at build time

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Date:   Mon, 11 Nov 2019 10:44:29 +0800
From:   Shile Zhang <shile.zhang@...ux.alibaba.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org
Subject: Re: [RFC PATCH 0/4] Speed booting by sorting ORC unwind tables at
 build time



On 2019/11/8 17:25, Peter Zijlstra wrote:
> On Fri, Nov 08, 2019 at 10:21:36AM +0100, Peter Zijlstra wrote:
>> On Fri, Nov 08, 2019 at 09:42:55AM +0800, Shile Zhang wrote:
>>
>>>> Can sort{ex,orc}table() be ran concurrently? Do they want to be the same
>>>> (threaded) tool?
>>> I think it is possible to do those sort work concurrently, likes deferred
>>> memory init which is big boot time speed up.
>>> But I don't know if the exception table and ORC unwind tables can be
>>> deferred, due to those tables might be used in early boot time, for early
>>> exception handling and early debugging. I'm not familiar with that.
>> I meant at link time, run both sorts concurrently such that we only have
>> to wait for the longest, instead of the sum of them.
>>
>> They're not changing the same part of the ELF file, so it should be
>> possible to have one tool have multiple threads, each sorting a
>> different table.
>>
>> Aside from the .ex_table and ORC there's also .jump_table that wants
>> sorting (see jump_label_sort_entries()).
> Oh, and I'll be adding .static_call_sites soon, see:
>
>    https://lkml.kernel.org/r/20191007082708.013939311@infradead.org
>
> (I should repost that)
>
> That gives us 4 tables to sort which we can do concurrently in 4
> threads.

I got your point now.
I'll try to rework the sort tool to sort all tables concurrently in one 
tool with multiple-threads.
Thanks for your advice!

>> I agree that doing it at link time makes sense, I just hate to do all
>> this sorting in sequence and blowing up the link time. I don't build for
>> customers, I build for single use boot and linking _SUCKS_.