From: Kiryl Shutsemau <kas@kernel.org>
To: Doug Anderson <dianders@chromium.org>
Cc: Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
James Morse <james.morse@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Marc Zyngier <maz@kernel.org>, Petr Mladek <pmladek@suse.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Baoquan He <bhe@redhat.com>,
Puranjay Mohan <puranjay@kernel.org>,
Usama Arif <usama.arif@linux.dev>,
Breno Leitao <leitao@debian.org>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Lecopzer Chen <lecopzer@gmail.com>,
Sumit Garg <sumit.garg@kernel.org>,
kernel-team@meta.com, kexec@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 0/4] arm64: cross-CPU NMI via SDEI
Date: Thu, 30 Jul 2026 16:50:17 +0100 [thread overview]
Message-ID: <amtyQH7lzLDKE3WD@thinkstation> (raw)
In-Reply-To: <CAD=FV=UN8+Yydm1G-afbaAfh2ZF7MzEE27UXoDOG0HFB0cwyXg@mail.gmail.com>
On Wed, Jul 29, 2026 at 02:37:37PM -0700, Doug Anderson wrote:
> Hi,
>
> On Tue, Jul 28, 2026 at 5:18 AM Kiryl Shutsemau <kas@kernel.org> wrote:
> >
> > The piece that isn't boot-time yet is the hardlockup detector that drives
> > all this. perf and buddy are mutually exclusive at compile time. We want
> > to use perf watchdog for FEAT_NMI while SDEI needs buddy.
>
> FWIW: can I ask why? You're worried about the "all CPUs lock up at the
> same time" problem? I am aware of some work towards solving that (even
> with buddy) by letting the hardware watchdog driver's "bark" interrupt
> run at NMI-level (or pseudo-NMI-level). With that change, I'm not
> aware of any benefits of the "perf" detector over the buddy one.
Honestly, no strong reason. I flagged perf mostly as "the detector you'd
reach for once NMIs are back", not from a concrete need.
The all-CPUs-wedge-at-once case is the only gap I was vaguely worried
about, since there's no live buddy left to notice it. If the NMI-level
bark work you mention closes that for buddy, then I don't see a reason to
want perf at all -- and as you say, buddy is cheaper.
Buddy everywhere would be strictly better for us.
--
Kiryl Shutsemau / Kirill A. Shutemov
prev parent reply other threads:[~2026-07-30 15:50 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-29 15:07 [PATCH v5 0/4] arm64: cross-CPU NMI via SDEI Kiryl Shutsemau
2026-06-29 15:07 ` [PATCH v5 1/4] firmware: arm_sdei: add sdei_is_present() Kiryl Shutsemau
2026-06-30 10:47 ` Usama Arif
2026-06-30 10:57 ` Kiryl Shutsemau
2026-06-29 15:07 ` [PATCH v5 2/4] firmware: arm_sdei: add SDEI_EVENT_SIGNAL support Kiryl Shutsemau
2026-06-30 10:51 ` Usama Arif
2026-06-30 10:58 ` Kiryl Shutsemau
2026-06-29 15:07 ` [PATCH v5 3/4] drivers/firmware: add SDEI cross-CPU NMI service for arm64 Kiryl Shutsemau
2026-06-29 15:07 ` [PATCH v5 4/4] arm64: escalate smp_send_stop() to an SDEI NMI as a last resort Kiryl Shutsemau
2026-07-03 6:01 ` [PATCH v5 0/4] arm64: cross-CPU NMI via SDEI YinFengwei
2026-07-09 16:16 ` Kiryl Shutsemau
2026-07-26 13:55 ` Will Deacon
2026-07-26 18:35 ` Kiryl Shutsemau
2026-07-28 10:25 ` Will Deacon
2026-07-28 12:17 ` Kiryl Shutsemau
2026-07-29 21:37 ` Doug Anderson
2026-07-30 15:50 ` Kiryl Shutsemau [this message]
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