linux-kernel - Re: [PATCH v8 9/9] x86/smpboot: Serialize topology updates for secondary bringup

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Message-ID: <BE9F9210-4DBD-4A9F-BA5A-A7B5BA580FCC@infradead.org>
Date:   Mon, 13 Feb 2023 21:53:15 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Usama Arif <usama.arif@...edance.com>, kim.phillips@....com
CC:     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,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH v8 9/9] x86/smpboot: Serialize topology updates for secondary bringup



On 13 February 2023 21:43:13 CET, Thomas Gleixner <tglx@...utronix.de> wrote:
>On Thu, Feb 09 2023 at 15:41, Usama Arif wrote:
>> From: David Woodhouse <dwmw@...zon.co.uk>
>>
>> The toplogy update is performed by the AP via smp_callin() after the BSP
>> has called do_wait_cpu_initialized(), setting the AP's bit in
>> cpu_callout_mask to allow it to proceed.
>>
>> In preparation to enable further parallelism of AP bringup, add locking to
>> serialize the update even if multiple APs are (in future) permitted to
>> proceed through the next stages of bringup in parallel.
>
>This one is also only relevant for further parallelisation, right?

I believe so, yes. But it's low-hanging fruit and might as well go in now.