Path: csiph.com!eternal-september.org!feeder.eternal-september.org!weretis.net!feeder1.news.weretis.net!newsfeed.CARNet.hr!news.spin.it!bofh.it!news.nic.it!robomod From: Wanpeng Li Newsgroups: linux.kernel Subject: [PATCH v4 2/3] KVM: dynamic halt_poll_ns adjustment Date: Thu, 27 Aug 2015 12:00:03 +0200 Message-ID: References: X-Original-To: Paolo Bonzini X-Tmn: [75Qj7BGhDq9tOscs+Vs09HCGFprMqyAQRhL8yNNvNIE=] X-Originating-Email: [wanpeng.li@hotmail.com] X-Mailer: git-send-email 1.9.1 X-Originalarrivaltime: 27 Aug 2015 09:52:35.0972 (UTC) FILETIME=[1A0CC440:01D0E0AE] MIME-Version: 1.0 Content-Type: text/plain Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 106 Organization: linux.* mail to news gateway X-Original-Cc: David Matlack , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Wanpeng Li X-Original-Date: Thu, 27 Aug 2015 17:52:18 +0800 X-Original-Message-ID: X-Original-References: <1440669139-2313-1-git-send-email-wanpeng.li@hotmail.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1214440 There is a downside of halt_poll_ns since poll is still happen for idle VCPU which can waste cpu usage. This patchset add the ability to adjust halt_poll_ns dynamically, grows halt_poll_ns if an interrupt arrives and shrinks halt_poll_ns when idle VCPU is detected. There are two new kernel parameters for changing the halt_poll_ns: halt_poll_ns_grow and halt_poll_ns_shrink. Test w/ high cpu overcommit ratio, pin vCPUs, and the halt_poll_ns of halt-poll is the default 500000ns, the max halt_poll_ns of dynamic halt-poll is 2ms. Then watch the %C0 in the dump of Powertop tool. The test method is almost from David. +-----------------+----------------+-------------------+ | | | | | w/o halt-poll | w/ halt-poll | dynamic halt-poll | +-----------------+----------------+-------------------+ | | | | | ~0.9% | ~1.8% | ~1.2% | +-----------------+----------------+-------------------+ The always halt-poll will increase ~0.9% cpu usage for idle vCPUs and the dynamic halt-poll drop it to ~0.3% which means that reduce the 67% overhead introduced by always halt-poll. Signed-off-by: Wanpeng Li --- virt/kvm/kvm_main.c | 41 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 40 insertions(+), 1 deletion(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index c06e57c..d63790d 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, 2ms is enough */ +static unsigned int halt_poll_ns = 2000000; 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; + + /* 500us step */ + if (val == 0 && halt_poll_ns_grow) + val = 500000; + 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)) { @@ -1961,6 +1995,11 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) cur = ktime_get(); out: + if (waited && vcpu->halt_poll_ns > 0) + shrink_halt_poll_ns(vcpu); + else if (vcpu->halt_poll_ns < halt_poll_ns) + grow_halt_poll_ns(vcpu); + trace_kvm_vcpu_wakeup(ktime_to_ns(cur) - ktime_to_ns(start), waited); } EXPORT_SYMBOL_GPL(kvm_vcpu_block); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/