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Fri, 13 Feb 2026 08:11:01 +0000 Date: Fri, 13 Feb 2026 08:11:01 +0000 Message-ID: <86h5rlawru.wl-maz@kernel.org> From: Marc Zyngier To: Colton Lewis Cc: kvm@vger.kernel.org, alexandru.elisei@arm.com, pbonzini@redhat.com, corbet@lwn.net, linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, mizhang@google.com, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, shuah@kernel.org, gankulkarni@os.amperecomputing.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-perf-users@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v6 00/19] ARM64 PMU Partitioning In-Reply-To: References: <86v7g5asp4.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: coltonlewis@google.com, kvm@vger.kernel.org, alexandru.elisei@arm.com, pbonzini@redhat.com, corbet@lwn.net, linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, mizhang@google.com, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, shuah@kernel.org, gankulkarni@os.amperecomputing.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-perf-users@vger.kernel.org, linux-kselftest@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false 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 Thu, 12 Feb 2026 21:08:36 +0000, Colton Lewis wrote: > > Hey Marc, thanks for the review. > > Marc Zyngier writes: > > > On Mon, 09 Feb 2026 22:13:55 +0000, > > Colton Lewis wrote: > > >> This series creates a new PMU scheme on ARM, a partitioned PMU that > >> allows reserving a subset of counters for more direct guest access, > >> significantly reducing overhead. More details, including performance > >> benchmarks, can be read in the v1 cover letter linked below. > > >> An overview of what this series accomplishes was presented at KVM > >> Forum 2025. Slides [1] and video [2] are linked below. > > >> IMPORTANT: This iteration does not yet implement the dynamic counter > >> reservation approach suggested by Will Deacon in January [3]. I am > >> working on it, but wanted to send this version first to keep momentum > >> going and ensure I've addressed all issues besides that. > > > [...] > > > As I have asked before, this is missing an example of how userspace is > > going to use this. Without it, it is impossible to correctly review > > this series. > > > Please consider this as a blocker. > > Understood. I remember you asking for a QEMU patch specifically. No. *any* VMM. QEMU, kvmtool, crosvm, firecrackpoter, whichever you want. > I had hoped that the use in the selftest was sufficient to show how to > use the uAPI. The selftests are absolutely pointless, like 99% of all selftests. They don't demonstrate how the userspace API works, now how configuring the PMU is ordered with the rest of the save/restore flow. > If not, I can send out an example QEMU patch to the QEMU ARM mailing > list. Please do. M. -- Without deviation from the norm, progress is not possible.