Messages in this thread | | | Subject | Re: [PATCH 3/3] KVM: s390: clear kicked_mask if not idle after set | From | Christian Borntraeger <> | Date | Wed, 20 Oct 2021 12:31:19 +0200 |
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Am 20.10.21 um 11:48 schrieb Michael Mueller: > > > On 19.10.21 19:54, Halil Pasic wrote: >> The idea behind kicked mask is that we should not re-kick a vcpu >> from __airqs_kick_single_vcpu() that is already in the middle of >> being kicked by the same function. >> >> If however the vcpu that was idle before when the idle_mask was >> examined, is not idle any more after the kicked_mask is set, that >> means that we don't need to kick, and that we need to clear the >> bit we just set because we may be beyond the point where it would >> get cleared in the wake-up process. Since the time window is short, >> this is probably more a theoretical than a practical thing: the race >> window is small. >> >> To get things harmonized let us also move the clear from vcpu_pre_run() >> to __unset_cpu_idle(). >> >> Signed-off-by: Halil Pasic <pasic@linux.ibm.com> >> Fixes: 9f30f6216378 ("KVM: s390: add gib_alert_irq_handler()") > > Before releasing something like this, where none of us is sure if > it really saves cpu cost, I'd prefer to run some measurement with > the whole kicked_mask logic removed and to compare the number of > vcpu wake ups with the number of interrupts to be processed by > the gib alert mechanism in a slightly over committed host while > driving with Matthews test load.
But I think patch 1 and 2 can go immediately as they measurably or testable fix things. Correct?
> A similar run can be done with this code. > >> --- >> arch/s390/kvm/interrupt.c | 7 ++++++- >> arch/s390/kvm/kvm-s390.c | 2 -- >> 2 files changed, 6 insertions(+), 3 deletions(-) >> >> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c >> index 2245f4b8d362..3c80a2237ef5 100644 >> --- a/arch/s390/kvm/interrupt.c >> +++ b/arch/s390/kvm/interrupt.c >> @@ -426,6 +426,7 @@ static void __unset_cpu_idle(struct kvm_vcpu *vcpu) >> { >> kvm_s390_clear_cpuflags(vcpu, CPUSTAT_WAIT); >> clear_bit(vcpu->vcpu_idx, vcpu->kvm->arch.idle_mask); >> + clear_bit(vcpu->vcpu_idx, vcpu->kvm->arch.gisa_int.kicked_mask); >> } >> static void __reset_intercept_indicators(struct kvm_vcpu *vcpu) >> @@ -3064,7 +3065,11 @@ static void __airqs_kick_single_vcpu(struct kvm *kvm, u8 deliverable_mask) >> /* lately kicked but not yet running */ >> if (test_and_set_bit(vcpu_idx, gi->kicked_mask)) >> return; >> - kvm_s390_vcpu_wakeup(vcpu); >> + /* if meanwhile not idle: clear and don't kick */ >> + if (test_bit(vcpu_idx, kvm->arch.idle_mask)) >> + kvm_s390_vcpu_wakeup(vcpu); >> + else >> + clear_bit(vcpu_idx, gi->kicked_mask); >> return; >> } >> } >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index 1c97493d21e1..6b779ef9f5fb 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -4067,8 +4067,6 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu) >> kvm_s390_patch_guest_per_regs(vcpu); >> } >> - clear_bit(vcpu->vcpu_idx, vcpu->kvm->arch.gisa_int.kicked_mask); >> - >> vcpu->arch.sie_block->icptcode = 0; >> cpuflags = atomic_read(&vcpu->arch.sie_block->cpuflags); >> VCPU_EVENT(vcpu, 6, "entering sie flags %x", cpuflags); >>
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