From patchwork Thu Sep 3 14:07:38 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wanpeng Li X-Patchwork-Id: 7119621 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 4ABE89F32B for ; Fri, 4 Sep 2015 00:12:12 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 612EC206FC for ; Fri, 4 Sep 2015 00:12:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 60F11206FB for ; Fri, 4 Sep 2015 00:12:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932805AbbIDALf (ORCPT ); Thu, 3 Sep 2015 20:11:35 -0400 Received: from blu004-omc1s2.hotmail.com ([65.55.116.13]:50424 "EHLO BLU004-OMC1S2.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932706AbbIDAL0 (ORCPT ); Thu, 3 Sep 2015 20:11:26 -0400 Received: from BLU436-SMTP201 ([65.55.116.8]) by BLU004-OMC1S2.hotmail.com over TLS secured channel with Microsoft SMTPSVC(7.5.7601.23008); Thu, 3 Sep 2015 17:11:25 -0700 X-TMN: [/30zbNPhL3yl5I1fEMgAbXRYxkLg1q7nYi6pUQHdgek=] X-Originating-Email: [wanpeng.li@hotmail.com] Message-ID: From: Wanpeng Li To: Paolo Bonzini CC: David Matlack , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Wanpeng Li Subject: [PATCH v7 2/3] KVM: dynamic halt-polling Date: Thu, 3 Sep 2015 22:07:38 +0800 X-Mailer: git-send-email 1.9.1 In-Reply-To: <1441289259-32072-1-git-send-email-wanpeng.li@hotmail.com> References: <1441289259-32072-1-git-send-email-wanpeng.li@hotmail.com> X-OriginalArrivalTime: 04 Sep 2015 00:11:23.0807 (UTC) FILETIME=[3BECAAF0:01D0E6A6] MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-5.4 required=5.0 tests=BAYES_00, DATE_IN_PAST_06_12, FREEMAIL_FROM,RCVD_IN_DNSWL_HI,T_RP_MATCHES_RCVD,UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP There is a downside of always-poll since poll is still happened for idle vCPUs which can waste cpu usage. This patchset add the ability to adjust halt_poll_ns dynamically, to grow halt_poll_ns when shot halt is detected, and to shrink halt_poll_ns when long halt is detected. There are two new kernel parameters for changing the halt_poll_ns: halt_poll_ns_grow and halt_poll_ns_shrink. no-poll always-poll dynamic-poll ----------------------------------------------------------------------- Idle (nohz) vCPU %c0 0.15% 0.3% 0.2% Idle (250HZ) vCPU %c0 1.1% 4.6%~14% 1.2% TCP_RR latency 34us 27us 26.7us "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 3.4%~12.8% CPUs/second and get close to no-polling overhead levels by using the dynamic-poll. The savings should be even higher for higher frequency ticks. Suggested-by: David Matlack Signed-off-by: Wanpeng Li --- virt/kvm/kvm_main.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 59 insertions(+), 4 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index c06e57c..d5e07e9 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -66,9 +66,18 @@ MODULE_AUTHOR("Qumranet"); MODULE_LICENSE("GPL"); -static unsigned int halt_poll_ns; +/* halt polling only reduces halt latency by 5-7 us, 500us is enough */ +static unsigned int halt_poll_ns = 500000; module_param(halt_poll_ns, uint, S_IRUGO | S_IWUSR); +/* Default doubles per-vcpu halt_poll_ns. */ +static unsigned int halt_poll_ns_grow = 2; +module_param(halt_poll_ns_grow, int, S_IRUGO); + +/* Default resets per-vcpu halt_poll_ns . */ +static unsigned int halt_poll_ns_shrink; +module_param(halt_poll_ns_shrink, int, S_IRUGO); + /* * Ordering of locks: * @@ -1907,6 +1916,31 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn) } EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty); +static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) +{ + int val = vcpu->halt_poll_ns; + + /* 10us base */ + if (val == 0 && halt_poll_ns_grow) + val = 10000; + else + val *= halt_poll_ns_grow; + + vcpu->halt_poll_ns = val; +} + +static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu) +{ + int val = vcpu->halt_poll_ns; + + if (halt_poll_ns_shrink == 0) + val = 0; + else + val /= halt_poll_ns_shrink; + + vcpu->halt_poll_ns = val; +} + static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu) { if (kvm_arch_vcpu_runnable(vcpu)) { @@ -1928,7 +1962,8 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) { ktime_t start, cur; DEFINE_WAIT(wait); - bool waited = false; + bool polled = false, waited = false; + u64 poll_ns = 0, wait_ns = 0, block_ns = 0; start = cur = ktime_get(); if (vcpu->halt_poll_ns) { @@ -1940,11 +1975,16 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) * arrives. */ if (kvm_vcpu_check_block(vcpu) < 0) { + polled = true; ++vcpu->stat.halt_successful_poll; - goto out; + break; } cur = ktime_get(); } while (single_task_running() && ktime_before(cur, stop)); + + poll_ns = ktime_to_ns(cur) - ktime_to_ns(start); + if (polled) + goto out; } for (;;) { @@ -1959,9 +1999,24 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) finish_wait(&vcpu->wq, &wait); cur = ktime_get(); + wait_ns = ktime_to_ns(cur) - ktime_to_ns(start); out: - trace_kvm_vcpu_wakeup(ktime_to_ns(cur) - ktime_to_ns(start), waited); + block_ns = poll_ns + wait_ns; + + if (halt_poll_ns) { + if (block_ns <= vcpu->halt_poll_ns) + ; + /* we had a long block, shrink polling */ + else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns) + shrink_halt_poll_ns(vcpu); + /* we had a short halt and our poll time is too small */ + else if (vcpu->halt_poll_ns < halt_poll_ns && + block_ns < halt_poll_ns) + grow_halt_poll_ns(vcpu); + } + + trace_kvm_vcpu_wakeup(block_ns, waited); } EXPORT_SYMBOL_GPL(kvm_vcpu_block);