From patchwork Thu Jan 16 12:44:20 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Borntraeger X-Patchwork-Id: 3498221 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id B2467C02DC for ; Thu, 16 Jan 2014 12:44:20 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 9AD7C20122 for ; Thu, 16 Jan 2014 12:44:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 56264200E9 for ; Thu, 16 Jan 2014 12:44:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752376AbaAPMoP (ORCPT ); Thu, 16 Jan 2014 07:44:15 -0500 Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:53889 "EHLO e06smtp13.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752287AbaAPMoN (ORCPT ); Thu, 16 Jan 2014 07:44:13 -0500 Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Thu, 16 Jan 2014 12:44:09 -0000 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 5BF301B08069; Thu, 16 Jan 2014 12:43:26 +0000 (GMT) Received: from d06av10.portsmouth.uk.ibm.com (d06av10.portsmouth.uk.ibm.com [9.149.37.251]) by b06cxnps4076.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s0GChp8e58195988; Thu, 16 Jan 2014 12:43:51 GMT Received: from d06av10.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av10.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s0GCi2Ni019060; Thu, 16 Jan 2014 05:44:03 -0700 Received: from tuxmaker.boeblingen.de.ibm.com (tuxmaker.boeblingen.de.ibm.com [9.152.85.9]) by d06av10.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVin) with ESMTP id s0GCi25N019057; Thu, 16 Jan 2014 05:44:02 -0700 Received: by tuxmaker.boeblingen.de.ibm.com (Postfix, from userid 25651) id 6FC9C12243AD; Thu, 16 Jan 2014 13:44:02 +0100 (CET) From: Christian Borntraeger To: Gleb Natapov , Paolo Bonzini Cc: KVM , linux-s390 , Cornelia Huck , Jens Freimann , agraf@suse.de, mst@redhat.com, Christian Borntraeger Subject: [PATCHv2/RFC] kvm/irqchip: Speed up KVM_SET_GSI_ROUTING Date: Thu, 16 Jan 2014 13:44:20 +0100 Message-Id: <1389876260-46636-1-git-send-email-borntraeger@de.ibm.com> X-Mailer: git-send-email 1.8.4.2 In-Reply-To: <52D7C186.1070700@redhat.com> References: <52D7C186.1070700@redhat.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14011612-2966-0000-0000-000009F505DE Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-7.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, 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 When starting lots of dataplane devices the bootup takes very long on my s390 system(prototype irqfd code). With larger setups we are even able to trigger some timeouts in some components. Turns out that the KVM_SET_GSI_ROUTING ioctl takes very long (strace claims up to 0.1 sec) when having multiple CPUs. This is caused by the synchronize_rcu and the HZ=100 of s390. By changing the code to use a private srcu we can speed things up. This patch reduces the boot time till mounting root from 8 to 2 seconds on my s390 guest with 100 disks. I converted most of the rcu routines to srcu. Review for the unconverted use of hlist_for_each_entry_rcu, hlist_add_head_rcu, hlist_del_init_rcu is necessary, though. They look fine to me since they are protected by outer functions. In addition, we should also discuss if a global srcu (for all guests) is fine. Signed-off-by: Christian Borntraeger --- virt/kvm/irqchip.c | 31 +++++++++++++++++-------------- 1 file changed, 17 insertions(+), 14 deletions(-) diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c index 20dc9e4..5283eb8 100644 --- a/virt/kvm/irqchip.c +++ b/virt/kvm/irqchip.c @@ -26,17 +26,20 @@ #include #include +#include #include #include #include "irq.h" +DEFINE_STATIC_SRCU(irq_srcu); + bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin) { struct kvm_irq_ack_notifier *kian; - int gsi; + int gsi, idx; - rcu_read_lock(); - gsi = rcu_dereference(kvm->irq_routing)->chip[irqchip][pin]; + idx = srcu_read_lock(&irq_srcu); + gsi = srcu_dereference(kvm->irq_routing, &irq_srcu)->chip[irqchip][pin]; if (gsi != -1) hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list, link) @@ -45,7 +48,7 @@ bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin) return true; } - rcu_read_unlock(); + srcu_read_unlock(&irq_srcu, idx); return false; } @@ -54,18 +57,18 @@ EXPORT_SYMBOL_GPL(kvm_irq_has_notifier); void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin) { struct kvm_irq_ack_notifier *kian; - int gsi; + int gsi, idx; trace_kvm_ack_irq(irqchip, pin); - rcu_read_lock(); - gsi = rcu_dereference(kvm->irq_routing)->chip[irqchip][pin]; + idx = srcu_read_lock(&irq_srcu); + gsi = srcu_dereference(kvm->irq_routing, &irq_srcu)->chip[irqchip][pin]; if (gsi != -1) hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list, link) if (kian->gsi == gsi) kian->irq_acked(kian); - rcu_read_unlock(); + srcu_read_unlock(&irq_srcu, idx); } void kvm_register_irq_ack_notifier(struct kvm *kvm, @@ -85,7 +88,7 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm, mutex_lock(&kvm->irq_lock); hlist_del_init_rcu(&kian->link); mutex_unlock(&kvm->irq_lock); - synchronize_rcu(); + synchronize_srcu_expedited(&irq_srcu); #ifdef __KVM_HAVE_IOAPIC kvm_vcpu_request_scan_ioapic(kvm); #endif @@ -115,7 +118,7 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level, bool line_status) { struct kvm_kernel_irq_routing_entry *e, irq_set[KVM_NR_IRQCHIPS]; - int ret = -1, i = 0; + int ret = -1, i = 0, idx; struct kvm_irq_routing_table *irq_rt; trace_kvm_set_irq(irq, level, irq_source_id); @@ -124,12 +127,12 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level, * IOAPIC. So set the bit in both. The guest will ignore * writes to the unused one. */ - rcu_read_lock(); - irq_rt = rcu_dereference(kvm->irq_routing); + idx = srcu_read_lock(&irq_srcu); + irq_rt = srcu_dereference(kvm->irq_routing, &irq_srcu); if (irq < irq_rt->nr_rt_entries) hlist_for_each_entry(e, &irq_rt->map[irq], link) irq_set[i++] = *e; - rcu_read_unlock(); + srcu_read_unlock(&irq_srcu, idx); while(i--) { int r; @@ -226,7 +229,7 @@ int kvm_set_irq_routing(struct kvm *kvm, kvm_irq_routing_update(kvm, new); mutex_unlock(&kvm->irq_lock); - synchronize_rcu(); + synchronize_srcu_expedited(&irq_srcu); new = old; r = 0;