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From: Thomas Gleixner <tglx@linutronix.de>
To: Brian Gerst <brgerst@gmail.com>, Usama Arif <usama.arif@bytedance.com>
Cc: dwmw2@infradead.org, kim.phillips@amd.com, arjan@linux.intel.com,
	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
Subject: Re: [PATCH v7 6/9] x86/smpboot: Support parallel startup of secondary CPUs
Date: Wed, 08 Feb 2023 14:13:18 +0100	[thread overview]
Message-ID: <87k00s2tch.ffs@tglx> (raw)
In-Reply-To: <CAMzpN2iejCnBeBdC6+92fUL2k8ZdAq_jEgXX+RSoGMhRZ0UBSA@mail.gmail.com>

On Wed, Feb 08 2023 at 00:09, Brian Gerst wrote:
> On Tue, Feb 7, 2023 at 6:10 PM Usama Arif <usama.arif@bytedance.com> wrote:
>> Introduce a global variable 'smpboot_control' indicating to the AP how
>> it should find its APIC ID. For a serialized bringup, the APIC ID is
>> explicitly passed in the low bits of smpboot_control, while for parallel
>> mode there are flags directing the AP to find its APIC ID in CPUID leaf
>> 0x0b (for X2APIC mode) or CPUID leaf 0x01 where 8 bits are sufficient.
>
> For the serialized bringup case, it would be simpler to just put the
> cpu number in the lower bits instead of the APIC id, skipping the
> lookup.

Yes and no. It can be done, but I rather prefer the consistency of the
data and the mechanism. The "overhead" or "win" is not even measurable.

Thanks,

        tglx

  parent reply	other threads:[~2023-02-08 13:13 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-07 23:04 [PATCH v7 0/9] Parallel CPU bringup for x86_64 Usama Arif
2023-02-07 23:04 ` [PATCH v7 1/9] x86/apic/x2apic: Allow CPU cluster_mask to be populated in parallel Usama Arif
2023-02-07 23:04 ` [PATCH v7 2/9] cpu/hotplug: Move idle_thread_get() to <linux/smpboot.h> Usama Arif
2023-02-07 23:04 ` [PATCH v7 3/9] cpu/hotplug: Add dynamic parallel bringup states before CPUHP_BRINGUP_CPU Usama Arif
2023-02-07 23:04 ` [PATCH v7 4/9] x86/smpboot: Reference count on smpboot_setup_warm_reset_vector() Usama Arif
2023-02-07 23:04 ` [PATCH v7 5/9] x86/smpboot: Split up native_cpu_up into separate phases and document them Usama Arif
2023-02-08 10:03   ` Yuan Yao
2023-02-08 12:02     ` David Woodhouse
2023-02-09  3:06       ` Yuan Yao
2023-02-07 23:04 ` [PATCH v7 6/9] x86/smpboot: Support parallel startup of secondary CPUs Usama Arif
2023-02-08  5:09   ` Brian Gerst
2023-02-08 12:54     ` [External] " Usama Arif
2023-02-08 12:56     ` David Woodhouse
2023-02-08 13:13     ` Thomas Gleixner [this message]
2023-02-08 14:41       ` David Woodhouse
2023-02-07 23:04 ` [PATCH v7 7/9] x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel Usama Arif
2023-02-07 23:04 ` [PATCH v7 8/9] x86/mtrr: Avoid repeated save of MTRRs on boot-time CPU bringup Usama Arif
2023-02-07 23:04 ` [PATCH v7 9/9] x86/smpboot: Serialize topology updates for secondary bringup Usama Arif
2023-02-09  3:53 ` [PATCH v7 0/9] Parallel CPU bringup for x86_64 Paul E. McKenney
2023-02-09  9:49   ` [External] " Usama Arif
2023-02-09 10:06     ` David Woodhouse
2023-02-09 10:19       ` Usama Arif
2023-02-09 10:22         ` David Woodhouse
2023-02-09 11:03     ` David Woodhouse
2023-02-09 11:45       ` Usama Arif
2023-02-09 11:53       ` Thomas Gleixner
2023-02-09 12:10         ` David Woodhouse
2023-02-09 13:48           ` David Woodhouse
2023-02-09 14:01             ` Usama Arif
2023-02-09 15:48           ` Thomas Gleixner

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