Date:   Thu, 16 Dec 2021 19:59:57 +0000
From:   David Woodhouse <dwmw2@infradead.org>
To:     Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>
CC:     Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "mimoja@mimoja.de" <mimoja@mimoja.de>,
        "hewenliang4@huawei.com" <hewenliang4@huawei.com>,
        "hushiyuan@huawei.com" <hushiyuan@huawei.com>,
        "luolongjun@huawei.com" <luolongjun@huawei.com>,
        "hejingxian@huawei.com" <hejingxian@huawei.com>
Subject: Re: [PATCH v3 0/9] Parallel CPU bringup for x86_64
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On 16 December 2021 19:55:36 GMT, Tom Lendacky <thomas=2Elendacky@amd=2Eco=
m> 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 f=
or
>>>> them shaves about 80% off the AP bringup time on a 96-thread socket
>>>> Skylake box (EC2 c5=2Emetal) =E2=80=94 from about 500ms to 100ms=2E
>>>>
>>>> There are more wins to be had with further parallelisation, but this =
is
>>>> the simple part=2E
>>>
>>> I applied this series and began booting a regular non-SEV guest and hi=
t a
>>> failure at 39 vCPUs=2E No panic or warning, just a reset and OVMF was
>>> executing again=2E I'll try to debug what's going, but not sure how qu=
ickly
>>> I'll arrive at anything=2E
>>=20
>> I've pushed the SEV-ES fix to
>> https://git=2Einfradead=2Eorg/users/dwmw2/linux=2Egit/shortlog/refs/hea=
ds/parallel-5=2E16
>> 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)=2E It would be interesting =
to
>> see if you can reproduce with just that much, both with and with
>> no_parallel_bringup=2E And then whether the subsequent commit that
>> actually enables the parallel INIT/SIPI/SIPI actually makes the
>> difference?
>>=20
>
>I'll pull it down and give it try=2E

Thanks=2E Note: don't use the whole thing; that last "parallel part2" patc=
h in particular isn't ready=2E And probably isn't where the next low-hangin=
g fruit is anyway=2E

--=20
Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E