linux-kernel - Re: [PATCH v6 00/11] Parallel CPU bringup for x86

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Message-ID: <3b626936ccc4d5123cb9113378bec6f77182def3.camel@infradead.org>
Date:   Mon, 06 Feb 2023 08:28:34 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Russ Anderson <rja@....com>, Usama Arif <usama.arif@...edance.com>
Cc:     tglx@...utronix.de, arjan@...ux.intel.com, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        x86@...nel.org, pbonzini@...hat.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        thomas.lendacky@....com, seanjc@...gle.com, pmenzel@...gen.mpg.de,
        fam.zheng@...edance.com, punit.agrawal@...edance.com,
        simon.evans@...edance.com, liangma@...ngbit.com
Subject: Re: [PATCH v6 00/11] Parallel CPU bringup for x86_64

On Sun, 2023-02-05 at 13:17 -0600, Russ Anderson wrote:
> 
> Gave the v6 patchset a try on a system with 1920 logocal cpus
> (sixteen 60 core Sapphire Rapids sockets with Hyperthreadding
> enabled).
> 
> Without the patchset it took 71 seconds to start all the cpus.
> With the v6 patchset it took 14 seconds to start all the cpus,
> a reduction of 57 seconds.  That is impressive.
> 
> Full boot, to root login prompt, without patches takes 223 seconds.
> This patchset reduces the full boot time by 57 seconds, a 25%
> reduction.

Nice; thanks for testing.

Is that with just the "part1" patch series which has been posted, or
also with the 'parallel part 2' still taking shape in the tree at
https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/parallel-6.2-rc6

I believe Usama said the second phase of parallelism didn't really help
much in terms of overall timing? Confirming that *without* all the
debug prints would be interesting. And we can look for what still
*could* be made parallel.

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