Message-ID: <e4350e62-b1b4-ad1f-d757-959dace44402@linux.intel.com>
Date:   Fri, 3 Feb 2023 06:41:50 -0800
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Subject: Re: [External] Re: [PATCH v6 06/11] x86/smpboot: Support parallel
 startup of secondary CPUs
To:     David Woodhouse <dwmw2@infradead.org>,
        Usama Arif <usama.arif@bytedance.com>, tglx@linutronix.de
Cc:     mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, x86@kernel.org, pbonzini@redhat.com,
        paulmck@kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de,
        hewenliang4@huawei.com, thomas.lendacky@amd.com, seanjc@google.com,
        pmenzel@molgen.mpg.de, fam.zheng@bytedance.com,
        punit.agrawal@bytedance.com, simon.evans@bytedance.com,
        liangma@liangbit.com
References: <20230202215625.3248306-1-usama.arif@bytedance.com>
 <20230202215625.3248306-7-usama.arif@bytedance.com>
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 <fb3e75fa-1a6f-0570-218f-ba9133fb72c6@bytedance.com>
 <fb72e7ae7b78e75a53acdb62960bdee8de5cb207.camel@infradead.org>
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From:   Arjan van de Ven <arjan@linux.intel.com>
In-Reply-To: <fb72e7ae7b78e75a53acdb62960bdee8de5cb207.camel@infradead.org>
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On 2/3/2023 12:14 AM, David Woodhouse wrote:
> On Thu, 2023-02-02 at 22:50 +0000, Usama Arif wrote:
>>
>> Ah, sorry about that, should have caught it while reviewing before
>> posting. To think of it, it might be better to squash this and next AMD
>> disabling patch, if anyone testing on AMD ever happens to check out at
>> this specific patch, their machine might not boot :).
>>
> 
> Nah, we don't actually *enable* parallel boot until the next patch
> anyway. At this point we're only laying the groundwork. I think it's
> best separate.
> 
>> Will repost only after getting the OK for the rest of the patches
>> along with addressing any other comments that come up.
> 
> Ack. And hopefully the missing SoB from both Thomas and Arjan for their
> parts. Part of the reasoning for the lack of SoB from Arjan might have
> been that we haven't finished doing the thinking about how this works
> in all cases, with non-constant TSC and other stuff. Let's make sure we
> give that a long hard stare.

most of it is that I need to sit down for some real time and have a think through it ;)

for all the common cases / modern HW it will be ok... but all the rest???

maybe we need a strict(er) safety valve on where this is used and then over time
widen the usage?

(after all, a regression means revert, and maybe it's better to only revert "add CPU type X" than
revert the whole series)