linux-kernel - Re: [PATCH v3 0/9] Parallel CPU bringup for x86

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Date:   Thu, 16 Dec 2021 19:59:57 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "mimoja@...oja.de" <mimoja@...oja.de>,
        "hewenliang4@...wei.com" <hewenliang4@...wei.com>,
        "hushiyuan@...wei.com" <hushiyuan@...wei.com>,
        "luolongjun@...wei.com" <luolongjun@...wei.com>,
        "hejingxian@...wei.com" <hejingxian@...wei.com>
Subject: Re: [PATCH v3 0/9] Parallel CPU bringup for x86_64



On 16 December 2021 19:55:36 GMT, Tom Lendacky <thomas.lendacky@....com> wrote:
>On 12/16/21 1:52 PM, David Woodhouse wrote:
>> On Thu, 2021-12-16 at 10:27 -0600, Tom Lendacky wrote:
>>> On 12/15/21 8:56 AM, David Woodhouse wrote:
>>>
>>>> Doing the INIT/SIPI/SIPI in parallel for all APs and *then* waiting for
>>>> them shaves about 80% off the AP bringup time on a 96-thread socket
>>>> Skylake box (EC2 c5.metal) — from about 500ms to 100ms.
>>>>
>>>> There are more wins to be had with further parallelisation, but this is
>>>> the simple part.
>>>
>>> I applied this series and began booting a regular non-SEV guest and hit a
>>> failure at 39 vCPUs. No panic or warning, just a reset and OVMF was
>>> executing again. I'll try to debug what's going, but not sure how quickly
>>> I'll arrive at anything.
>> 
>> I've pushed the SEV-ES fix to
>> https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/parallel-5.16
>> and in doing so I've moved the 'no_parallel_bringup' command line
>> argument earlier in the series, to Thomas's "Support parallel startup
>> of secondary CPUs" commit (now 191f0899757). It would be interesting to
>> see if you can reproduce with just that much, both with and with
>> no_parallel_bringup. And then whether the subsequent commit that
>> actually enables the parallel INIT/SIPI/SIPI actually makes the
>> difference?
>> 
>
>I'll pull it down and give it try.

Thanks. Note: don't use the whole thing; that last "parallel part2" patch in particular isn't ready. And probably isn't where the next low-hanging fruit is anyway.

-- 
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