From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753114AbbIAVlg (ORCPT ); Tue, 1 Sep 2015 17:41:36 -0400 Received: from mail-pa0-f50.google.com ([209.85.220.50]:36662 "EHLO mail-pa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752300AbbIAVle (ORCPT ); Tue, 1 Sep 2015 17:41:34 -0400 From: David Matlack To: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, pbonzini@redhat.com, wanpeng.li@hotmail.com, peter@kieser.ca, David Matlack Subject: [PATCH 0/2] Adaptive halt-polling toggle Date: Tue, 1 Sep 2015 14:41:14 -0700 Message-Id: <1441143676-9375-1-git-send-email-dmatlack@google.com> X-Mailer: git-send-email 2.5.0.457.gab17608 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patchset adds a dynamic on/off switch for polling. This patchset gets good performance on its own for both idle and Message Passing workloads. no-poll always-poll adaptive-toggle --------------------------------------------------------------------- Idle (nohz) VCPU %c0 0.12 0.32 0.15 Idle (250HZ) VCPU %c0 1.22 6.35 1.27 TCP_RR latency 39 us 25 us 25 us (3.16 Linux guest, halt_poll_ns=200000) "Idle (X) VCPU %c0" is the percent of time the physical cpu spent in c0 over 60 seconds (each VCPU is pinned to a PCPU). (nohz) means the guest was tickless. (250HZ) means the guest was ticking at 250HZ. The big win is with ticking operating systems. Running the linux guest with nohz=off (and HZ=250), we save 5% CPUs/second and get close to no-polling overhead levels by using the adaptive toggle. The savings should be even higher for higher frequency ticks. Since we get low idle overhead with polling now, halt_poll_ns defaults to 200000, instead of 0. We can increase halt_poll_ns a bit more once we have dynamic halt-polling length adjustments (Wanpeng's patch). We should however keep halt_poll_ns below 1 ms since that is the tick frequency used by windows. David Matlack (1): kvm: adaptive halt-polling toggle Wanpeng Li (1): KVM: make halt_poll_ns per-VCPU include/linux/kvm_host.h | 1 + include/trace/events/kvm.h | 23 ++++++---- virt/kvm/kvm_main.c | 111 ++++++++++++++++++++++++++++++++++----------- 3 files changed, 99 insertions(+), 36 deletions(-) -- 2.5.0.457.gab17608