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

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Date:   Thu, 16 Dec 2021 13:55:36 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     David Woodhouse <dwmw2@...radead.org>,
        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 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,
Tom

> Thanks!
>