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Fri, 25 Sep 2026 10:04:35 +0000 (GMT) Received: from [9.224.77.173] (unknown [9.224.77.173]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 25 Sep 2026 10:04:35 +0000 (GMT) Message-ID: <2988db19-755c-445a-8226-95e99904a232@linux.ibm.com> Date: Fri, 25 Sep 2026 12:04:34 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/3] KVM: s390: Add opportunistic floating IRQ injection To: Janosch Frank , kvm@vger.kernel.org Cc: imbrenda@linux.ibm.com, linux-s390@vger.kernel.org, pasic@linux.ibm.com References: <20260820121546.24694-1-frankja@linux.ibm.com> <20260820121546.24694-4-frankja@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20260820121546.24694-4-frankja@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: O5I6YfGGPWqZnPiSTJXIYky6VYSR-Mw8 X-Authority-Analysis: v=2.4 cv=EOCTQFZC c=1 sm=1 tr=0 ts=6ab64738 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VnNF1IyMAAAA:8 a=4WfngMj7Zh_IP9iRE-IA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTI1MDAzOCBTYWx0ZWRfXxdLnUQ4OBB1l 78xFHL2I/sHbpxr8Lethg/fbeEAHJBDYueOWNOxBa5OIKUQl7d528gF5Hasf8iBmSeE4TZhR0VG YAzJ/Gp9H/3+5rdFoP2opkjvSigDR7Y= X-Proofpoint-GUID: O5I6YfGGPWqZnPiSTJXIYky6VYSR-Mw8 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTI1MDAzOCBTYWx0ZWRfXyT9KUhy8zwBa hOq9MmkhvaIcTseN52tdFJEjy9nKBed66b5SGg2EWZ+jHNjbHpeTZ4wf2iUOsFGXnnVZpvx5Ni6 NI93l8eJax0SeqmV0CcsGC7b4HlKOx6X7nfvcGJXJOKmDNV/L+HIzJNgbn4wsxz2nzvuP2lIaNh cLPzdXQqVZdc/Cz+XfOY0iAF1AQq4+0/FmFmJ6Q7Cxgqi0mO6bYkHPaY2Iw/YZyyHgU5JPTVyeB oY1PsgV4NHjycGmaswLyljHcgK36vsQUlrIX/coK4xAyH+Il4QSHHS715O6x4kwLjNQPC5rUrdf +QQ7PAa6CecPXEGPBQhrAbuImxU8BzLAOXQMr/1WSkNJdpYd7lYKdlJ7VsN7oX1wRXxPvF7YPd0 aCI+cdZMujxfPKFXYJsJsh/765E1M7UzEoEddh3woa6V+0U0EmCBgexU0vJFrL95S+DF0FrexOs NJJToujqdnUa5kZVfcw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-25_02,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 phishscore=0 priorityscore=1501 clxscore=1015 spamscore=0 adultscore=0 impostorscore=0 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609250038 Am 20.08.26 um 14:12 schrieb Janosch Frank: > Try to distribute floating IRQs which haven't been taken by a VCPU yet > to sleeping VCPUs. This lowers the risk of floating IRQs not being > delivered. I think this could be too expensive in the innermost loop. As an alternative: what about actually adding a check in handle wait that triggers if we are going to sleep despite pending interrupts.> > Signed-off-by: Janosch Frank > --- > arch/s390/include/asm/kvm_host.h | 1 + > arch/s390/kvm/interrupt.c | 31 +++++++++++++++++++++++++++++++ > arch/s390/kvm/kvm-s390.c | 3 +++ > arch/s390/kvm/kvm-s390.h | 1 + > 4 files changed, 36 insertions(+) > > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h > index b4182ca4435f..1d62bdd7aca5 100644 > --- a/arch/s390/include/asm/kvm_host.h > +++ b/arch/s390/include/asm/kvm_host.h > @@ -467,6 +467,7 @@ struct kvm_vm_stat { > u64 gmap_shadow_r3_entry; > u64 gmap_shadow_sg_entry; > u64 gmap_shadow_pg_entry; > + u64 inject_redist; > }; > > struct kvm_arch_memory_slot { > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index b3e4bfeacff2..54f20347f553 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -367,6 +367,37 @@ static unsigned long deliverable_irqs(struct kvm_vcpu *vcpu) > return active_mask; > } > > +void distribute_float_irqs(struct kvm *kvm) > +{ > + struct kvm_vcpu *dst_vcpu; > + int sigcpu, online_vcpus; > + > + if (!READ_ONCE(kvm->arch.float_int.pending_irqs)) > + return; > + > + online_vcpus = atomic_read(&kvm->online_vcpus); > + > + /* > + * Not too worried about synchronization for idle_mask. We > + * might burn too many cycles but apart from that waking a > + * vcpu is not harmful. > + */ > + sigcpu = find_first_bit(kvm->arch.idle_mask, online_vcpus); > + /* Well nobody's sleeping so someone will likely take the IRQ soon */ > + if (sigcpu == online_vcpus) > + return; > + > + do { > + dst_vcpu = kvm_get_vcpu(kvm, sigcpu); > + if (deliverable_irqs(dst_vcpu)) { > + kvm->stat.inject_redist++; > + kvm_s390_vcpu_wakeup(dst_vcpu); > + break; > + } > + sigcpu = find_next_bit(kvm->arch.idle_mask, online_vcpus, ++sigcpu); > + } while (sigcpu < online_vcpus); > +} > + > static void __set_cpu_idle(struct kvm_vcpu *vcpu) > { > kvm_s390_set_cpuflags(vcpu, CPUSTAT_WAIT); > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 518a69c55e85..d6d46688d980 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -86,6 +86,7 @@ const struct kvm_stats_desc kvm_vm_stats_desc[] = { > STATS_DESC_COUNTER(VM, gmap_shadow_r3_entry), > STATS_DESC_COUNTER(VM, gmap_shadow_sg_entry), > STATS_DESC_COUNTER(VM, gmap_shadow_pg_entry), > + STATS_DESC_COUNTER(VM, inject_redist), > }; > > const struct kvm_stats_header kvm_vm_stats_header = { > @@ -4572,6 +4573,8 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu) > rc = kvm_s390_deliver_pending_interrupts(vcpu); > if (rc || guestdbg_exit_pending(vcpu)) > return rc; > + > + distribute_float_irqs(vcpu->kvm); > } > > rc = kvm_s390_handle_requests(vcpu); > diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h > index 8e886bcef4a0..7115a8f5b188 100644 > --- a/arch/s390/kvm/kvm-s390.h > +++ b/arch/s390/kvm/kvm-s390.h > @@ -376,6 +376,7 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu); > void kvm_s390_clear_local_irqs(struct kvm_vcpu *vcpu); > void kvm_s390_clear_float_irqs(struct kvm *kvm); > void kvm_s390_pv_sclp_kick(struct kvm_vcpu *vcpu); > +void distribute_float_irqs(struct kvm *kvm); > int __must_check kvm_s390_inject_vm(struct kvm *kvm, > struct kvm_s390_interrupt *s390int, > struct kvm_s390_interrupt_info *inti);