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

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Date:   Thu, 16 Dec 2021 19:24:56 +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,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        hushiyuan@...wei.com, luolongjun@...wei.com, hejingxian@...wei.com
Subject: Re: [PATCH v3 0/9] Parallel CPU bringup for x86_64

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.

Thanks for testing. This is working for me with BIOS and EFI boots in
qemu and real hardware but it's mostly been Intel so far. I'll try
harder on an AMD box.

Anything else special about your setup, kernel config or qemu
invocation that might help me reproduce?

If it can repro without KVM, 'qemu -d in_asm' can be extremely useful
for this kind of thing btw.

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