From patchwork Wed Sep 2 07:29:30 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wanpeng Li X-Patchwork-Id: 7108911 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 4412A9F1CD for ; Wed, 2 Sep 2015 07:30:17 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 56FB8204EC for ; Wed, 2 Sep 2015 07:30:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5949720603 for ; Wed, 2 Sep 2015 07:30:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753163AbbIBHaH (ORCPT ); Wed, 2 Sep 2015 03:30:07 -0400 Received: from blu004-omc1s38.hotmail.com ([65.55.116.49]:64648 "EHLO BLU004-OMC1S38.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753040AbbIBHaE (ORCPT ); Wed, 2 Sep 2015 03:30:04 -0400 Received: from BLU436-SMTP50 ([65.55.116.7]) by BLU004-OMC1S38.hotmail.com over TLS secured channel with Microsoft SMTPSVC(7.5.7601.23008); Wed, 2 Sep 2015 00:30:03 -0700 X-TMN: [xfPP3qsfcktmzqQo2zOh5CEJ9euLuGPUKcI/c8mUA4E=] 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 v6 2/3] KVM: dynamic halt_poll_ns adjustment Date: Wed, 2 Sep 2015 15:29:30 +0800 X-Mailer: git-send-email 1.9.1 In-Reply-To: <1441178971-3836-1-git-send-email-wanpeng.li@hotmail.com> References: <1441178971-3836-1-git-send-email-wanpeng.li@hotmail.com> X-OriginalArrivalTime: 02 Sep 2015 07:30:01.0767 (UTC) FILETIME=[2DD32B70:01D0E551] 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=-6.9 required=5.0 tests=BAYES_00,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 patch adds 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 | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 58 insertions(+), 3 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index c06e57c..3cff02f 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)) { @@ -1929,6 +1963,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) ktime_t start, cur; DEFINE_WAIT(wait); bool waited = false; + u64 poll_ns = 0, wait_ns = 0, block_ns = 0; start = cur = ktime_get(); if (vcpu->halt_poll_ns) { @@ -1941,10 +1976,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) */ if (kvm_vcpu_check_block(vcpu) < 0) { ++vcpu->stat.halt_successful_poll; - goto out; + break; } cur = ktime_get(); } while (single_task_running() && ktime_before(cur, stop)); + + if (ktime_before(cur, stop)) { + poll_ns = ktime_to_ns(cur) - ktime_to_ns(start); + 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);