From: Thomas Gleixner <tglx@kernel.org>
To: Jinjie Ruan <ruanjinjie@huawei.com>,
Michael Kelley <mhklinux@outlook.com>,
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Subject: Re: [PATCH RFC 3/3] arm64: Add HOTPLUG_PARALLEL support for secondary CPUs
Date: Thu, 18 Jun 2026 17:53:41 +0200 [thread overview]
Message-ID: <874iizdeuy.ffs@fw13> (raw)
In-Reply-To: <4588efb4-e757-4ca7-9197-025b67ca9ef6@huawei.com>
On Mon, Jun 15 2026 at 17:57, Jinjie Ruan wrote:
> On 6/12/2026 11:45 PM, Michael Kelley wrote:
>
> - Default (no patch): Slowest HVC64 handling (126 μs), highest WFx count
> (85k), and most total VM‑exits.
>
> - cpuhp.parallel=1: HVC64 latency improved to 78 μs (close to
> cpuhp.parallel=0), but IRQ exits increased dramatically (12.9k, 2.7×
> that of `cpuhp.parallel=0`), accounting for 95% of event time and
> becoming the new bottleneck.
>
> - cpuhp.parallel=0: Fastest HVC64 (69 μs), lowest IRQ exits (4.8k), and
> lowest total samples, delivering the best overall boot performance.
>
> Therefor, `cpuhp.parallel=1` reduces HVC cost but suffers from a massive
> increase in IRQ exits, while `cpuhp.parallel=0` avoids this interrupt
> storm and therefore performs best in a KVM guest.
What's the cause for having this massive interrupt exit rate in parallel
mode? Just because parallel does not give a useful explanation.
Thanks,
tglx
next prev parent reply other threads:[~2026-06-18 16:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-11 13:38 [PATCH RFC 0/3] arm64: Add HOTPLUG_PARALLEL support for secondary CPUs Jinjie Ruan
2026-06-11 13:38 ` [PATCH RFC 1/3] cpu/hotplug: Introduce CONFIG_PARALLEL_SMT_PRIMARY_FIRST Jinjie Ruan
2026-06-18 15:17 ` Thomas Gleixner
2026-06-11 13:38 ` [PATCH RFC 2/3] arm64: smp: Pass CPU ID to update_cpu_boot_status() Jinjie Ruan
2026-06-11 13:38 ` [PATCH RFC 3/3] arm64: Add HOTPLUG_PARALLEL support for secondary CPUs Jinjie Ruan
2026-06-12 15:45 ` Michael Kelley
2026-06-15 8:51 ` Jinjie Ruan
2026-06-18 12:21 ` Will Deacon
2026-06-15 9:57 ` Jinjie Ruan
2026-06-18 15:53 ` Thomas Gleixner [this message]
2026-06-18 15:49 ` Thomas Gleixner
2026-06-12 15:51 ` [PATCH RFC 0/3] " Michael Kelley
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