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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1waF3q-00000001X57-23A3; Thu, 18 Jun 2026 15:53:46 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1waF3p-00000001X4l-0iZd; Thu, 18 Jun 2026 15:53:45 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 60A5460018; Thu, 18 Jun 2026 15:53:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D5851F000E9; Thu, 18 Jun 2026 15:53:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781798024; bh=EwX9mxVgUx4kbF0qZ290eryMIgfNI0MdhJKVS5zuxOw=; h=From:To:Subject:In-Reply-To:References:Date; b=dFbyuhdxS8KRLeKukg6wGxWrZKR7+kw+xqNzs3yRunvw4FB7RQT+K+h6r1RUTVb4a H+XMDkYxvmBiMuqK6N4j1KwALKy4zAVPDNJLrqk5VRjQmKqdBxJSdrP0h3D/m/mb/Y 08qVUbjX3v5xmk5PeWvmWNQ7NBaxuUDFHMnmx8qih+TsRiJYrLNTg9orqijFMNJ/zY UYIpbgfnw2o6Wu/fRmaGf38lG5t4n+Y8avnbK9JaZ9rWD+u7xO68HArQRZjlEQIK/U yTyHP2EioUBOSUKbMp9/bDNibaJlaph6Xa8ztrGG4/FL5Ju36LIJsfYUCim8Oa3P8+ UMWh6Gg9zlbNA== From: Thomas Gleixner To: Jinjie Ruan , Michael Kelley , "catalin.marinas@arm.com" , "will@kernel.org" , "tsbogend@alpha.franken.de" , "pjw@kernel.org" , "palmer@dabbelt.com" , "aou@eecs.berkeley.edu" , "alex@ghiti.fr" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "hpa@zytor.com" , "peterz@infradead.org" , "kees@kernel.org" , "nathan@kernel.org" , "linusw@kernel.org" , "ojeda@kernel.org" , "david.kaplan@amd.com" , "lukas.bulwahn@redhat.com" , "ryan.roberts@arm.com" , "maz@kernel.org" , "timothy.hayes@arm.com" , "lpieralisi@kernel.org" , "thuth@redhat.com" , "oupton@kernel.org" , "yeoreum.yun@arm.com" , "miko.lenczewski@arm.com" , "broonie@kernel.org" , "kevin.brodsky@arm.com" , "james.clark@linaro.org" , "tabba@google.com" , "mrigendra.chaubey@gmail.com" , "arnd@arndb.de" , "anshuman.khandual@arm.com" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mips@vger.kernel.org" , "linux-riscv@lists.infradead.org" Subject: Re: [PATCH RFC 3/3] arm64: Add HOTPLUG_PARALLEL support for secondary CPUs In-Reply-To: <4588efb4-e757-4ca7-9197-025b67ca9ef6@huawei.com> References: <20260611133809.3854977-1-ruanjinjie@huawei.com> <20260611133809.3854977-4-ruanjinjie@huawei.com> <4588efb4-e757-4ca7-9197-025b67ca9ef6@huawei.com> Date: Thu, 18 Jun 2026 17:53:41 +0200 Message-ID: <874iizdeuy.ffs@fw13> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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=E2=80=AF=CE=BCs), highe= st WFx count > (85k), and most total VM=E2=80=91exits. > > - cpuhp.parallel=3D1: HVC64 latency improved to 78=E2=80=AF=CE=BCs (close= to > cpuhp.parallel=3D0), but IRQ exits increased dramatically (12.9k, 2.7=C3= =97 > that of `cpuhp.parallel=3D0`), accounting for 95% of event time and > becoming the new bottleneck. > > - cpuhp.parallel=3D0: Fastest HVC64 (69=E2=80=AF=CE=BCs), lowest IRQ exit= s (4.8k), and > lowest total samples, delivering the best overall boot performance. > > Therefor, `cpuhp.parallel=3D1` reduces HVC cost but suffers from a massive > increase in IRQ exits, while `cpuhp.parallel=3D0` 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