Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754460AbdHUUih (ORCPT ); Mon, 21 Aug 2017 16:38:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34410 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753985AbdHUUic (ORCPT ); Mon, 21 Aug 2017 16:38:32 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 9AF3AC0587FE Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=rkrcmar@redhat.com From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-mips@linux-mips.org, kvm-ppc@vger.kernel.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: Paolo Bonzini , David Hildenbrand , Christoffer Dall , Marc Zyngier , Christian Borntraeger , Cornelia Huck , James Hogan , Paul Mackerras , Alexander Graf Subject: [PATCH RFC v3 6/9] KVM: rework kvm_vcpu_on_spin loop Date: Mon, 21 Aug 2017 22:35:27 +0200 Message-Id: <20170821203530.9266-7-rkrcmar@redhat.com> In-Reply-To: <20170821203530.9266-1-rkrcmar@redhat.com> References: <20170821203530.9266-1-rkrcmar@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 21 Aug 2017 20:38:32 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3262 Lines: 105 The original code managed to obfuscate a straightforward idea: start iterating from the selected index and reset the index to 0 when reaching the end of online vcpus, then iterate until reaching the index that we started at. The resulting code is a bit better, IMO. (Still horrible, though.) Signed-off-by: Radim Krčmář --- include/linux/kvm_host.h | 13 +++++++++++++ virt/kvm/kvm_main.c | 47 ++++++++++++++++++----------------------------- 2 files changed, 31 insertions(+), 29 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index abd5cb1feb9e..cfb3c0efdd51 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -498,6 +498,19 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i) (vcpup = kvm_get_vcpu(kvm, idx)) != NULL; \ idx++) +#define kvm_for_each_vcpu_from(idx, vcpup, from, kvm) \ + for (idx = from, vcpup = kvm_get_vcpu(kvm, idx); \ + vcpup; \ + ({ \ + idx++; \ + if (idx >= atomic_read(&kvm->online_vcpus)) \ + idx = 0; \ + if (idx == from) \ + vcpup = NULL; \ + else \ + vcpup = kvm_get_vcpu(kvm, idx); \ + })) + static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id) { struct kvm_vcpu *vcpu = NULL; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index d89261d0d8c6..33a15e176927 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2333,8 +2333,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode) struct kvm_vcpu *vcpu; int last_boosted_vcpu = me->kvm->last_boosted_vcpu; int yielded = 0; - int try = 3; - int pass; + int try = 2; int i; kvm_vcpu_set_in_spin_loop(me, true); @@ -2345,34 +2344,24 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode) * VCPU is holding the lock that we need and will release it. * We approximate round-robin by starting at the last boosted VCPU. */ - for (pass = 0; pass < 2 && !yielded && try; pass++) { - kvm_for_each_vcpu(i, vcpu, kvm) { - if (!pass && i <= last_boosted_vcpu) { - i = last_boosted_vcpu; - continue; - } else if (pass && i > last_boosted_vcpu) - break; - if (!ACCESS_ONCE(vcpu->preempted)) - continue; - if (vcpu == me) - continue; - if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu)) - continue; - if (yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu)) - continue; - if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) - continue; + kvm_for_each_vcpu_from(i, vcpu, last_boosted_vcpu, kvm) { + if (!ACCESS_ONCE(vcpu->preempted)) + continue; + if (vcpu == me) + continue; + if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu)) + continue; + if (yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu)) + continue; + if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) + continue; - yielded = kvm_vcpu_yield_to(vcpu); - if (yielded > 0) { - kvm->last_boosted_vcpu = i; - break; - } else if (yielded < 0) { - try--; - if (!try) - break; - } - } + yielded = kvm_vcpu_yield_to(vcpu); + if (yielded > 0) { + kvm->last_boosted_vcpu = i; + break; + } else if (yielded < 0 && !try--) + break; } kvm_vcpu_set_in_spin_loop(me, false); -- 2.13.3