From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 829D8C43331 for ; Thu, 7 Nov 2019 16:04:29 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 459EB218AE for ; Thu, 7 Nov 2019 16:04:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 459EB218AE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id CB3034ACA7; Thu, 7 Nov 2019 11:04:28 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id F2Fj8e1eH8G4; Thu, 7 Nov 2019 11:04:27 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id CA8874ACA5; Thu, 7 Nov 2019 11:04:26 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id B93FE4ACAB for ; Thu, 7 Nov 2019 11:04:25 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 8vpleHFXA1p5 for ; Thu, 7 Nov 2019 11:04:24 -0500 (EST) Received: from inca-roads.misterjones.org (inca-roads.misterjones.org [213.251.177.50]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 92B534AC83 for ; Thu, 7 Nov 2019 11:04:24 -0500 (EST) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.lan) by cheepnis.misterjones.org with esmtpsa (TLSv1.2:DHE-RSA-AES128-GCM-SHA256:128) (Exim 4.80) (envelope-from ) id 1iSkGk-0008Bm-6O; Thu, 07 Nov 2019 17:04:22 +0100 From: Marc Zyngier To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Subject: [PATCH 0/2] KVM: arm64: Reduce occurence of GICv4 doorbells on non-oversubscribed systems Date: Thu, 7 Nov 2019 16:04:10 +0000 Message-Id: <20191107160412.30301-1-maz@kernel.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu As I was cleaning up some of the GICv4 code to make way for GICv4.1 it occured to me that we could drastically reduce the impact of the GICv4 doorbells on systems that are not oversubscribed (each vcpu "owns" a physical CPU). The technique borrows its logic from the way we disable WFE trapping when a vcpu is the only process on the CPU run-queue. If this vcpu is the target of VLPIs, it is then beneficial not to trap blocking WFIs and to leave the vcpu waiting for interrupts in guest state. All we need to do here is to track whether VLPIs are associated to a vcpu (which is easily done by using a counter that we update on MAPI, DISCARD and MOVI). It has been *very lightly* tested on a D05, and behaved pretty well in my limited test cases (I get almost no doorbell at all in the non oversubscribed case, and the usual hailstorm as soon as there is oversubscription). I'd welcome some testing on more current HW. Marc Zyngier (2): KVM: vgic-v4: Track the number of VLPIs per vcpu KVM: arm64: Opportunistically turn off WFI trapping when using direct LPI injection arch/arm/include/asm/kvm_emulate.h | 4 ++-- arch/arm64/include/asm/kvm_emulate.h | 9 +++++++-- include/linux/irqchip/arm-gic-v4.h | 2 ++ virt/kvm/arm/arm.c | 4 ++-- virt/kvm/arm/vgic/vgic-init.c | 1 + virt/kvm/arm/vgic/vgic-its.c | 3 +++ virt/kvm/arm/vgic/vgic-v4.c | 2 ++ 7 files changed, 19 insertions(+), 6 deletions(-) -- 2.20.1 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm