From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: [PATCH RFC] ACPI: disable extra P_LVLx access on KVM Date: Fri, 30 Mar 2018 20:43:58 +0300 Message-ID: <1522431741-4678-1-git-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , kvm@vger.kernel.org, "Rafael J. Wysocki" , Len Brown , linux-acpi@vger.kernel.org List-Id: linux-acpi@vger.kernel.org As documented by commit b488f021 "ACPI: restore comment justifying 'extra' P_LVLx access", Linux does an extra IO read after entering idle because on (some) chipsets STPCLK# doesn't get asserted in time to prevent further instruction processing. This can never be the case on KVM, and a timer read causes an expensive VM exit in turn causing useless load on host system. Detect KVM and skip the read. TODO: whitelist more hypervisors? Note: very lightly tested. Pls don't apply this yet, I am working on a _CST implementation for KVM and will repost this without the RFC tag when it's been tested properly. Posting now for early flames/feedback. Cc: Paolo Bonzini Cc: Radim Krčmář Cc: kvm@vger.kernel.org Signed-off-by: Michael S. Tsirkin --- drivers/acpi/processor_idle.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index abb559c..8ae28dc 100644 --- a/drivers/acpi/processor_idle.c +++ b/drivers/acpi/processor_idle.c @@ -33,6 +33,7 @@ #include #include #include +#include /* * Include the apic definitions for x86 to have the APIC timer related defines @@ -665,7 +666,8 @@ static void __cpuidle acpi_idle_do_entry(struct acpi_processor_cx *cx) /* Dummy wait op - must do something useless after P_LVL2 read because chipsets cannot guarantee that STPCLK# signal gets asserted in time to freeze execution properly. */ - inl(acpi_gbl_FADT.xpm_timer_block.address); + if (!kvm_para_available()) + inl(acpi_gbl_FADT.xpm_timer_block.address); } } @@ -687,7 +689,8 @@ static int acpi_idle_play_dead(struct cpuidle_device *dev, int index) else if (cx->entry_method == ACPI_CSTATE_SYSTEMIO) { inb(cx->address); /* See comment in acpi_idle_do_entry() */ - inl(acpi_gbl_FADT.xpm_timer_block.address); + if (!kvm_para_available()) + inl(acpi_gbl_FADT.xpm_timer_block.address); } else return -ENODEV; } -- MST