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KVM: Optimize kvm_make_vcpus_request_mask() a bit

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Iterating over set bits in 'vcpu_bitmap' should be faster than going
through all vCPUs, especially when just a few bits are set.

Drop kvm_make_vcpus_request_mask() call from kvm_make_all_cpus_request_except()
to avoid handling the special case when 'vcpu_bitmap' is NULL, move the
code to kvm_make_all_cpus_request_except() itself.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210903075141.403071-5-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2021-09-03 09:51:37 +02:00 committed by Paolo Bonzini
parent 6470accc7b
commit ae0946cd36
1 changed files with 53 additions and 35 deletions
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88
virt/kvm/kvm_main.c
View file

@ -251,50 +251,57 @@ static inline bool kvm_kick_many_cpus(cpumask_var_t tmp, bool wait)
return true;
}
static void kvm_make_vcpu_request(struct kvm *kvm, struct kvm_vcpu *vcpu,
unsigned int req, cpumask_var_t tmp,
int current_cpu)
{
int cpu;
kvm_make_request(req, vcpu);
if (!(req & KVM_REQUEST_NO_WAKEUP) && kvm_vcpu_wake_up(vcpu))
return;
/*
* tmp can be "unavailable" if cpumasks are allocated off stack as
* allocation of the mask is deliberately not fatal and is handled by
* falling back to kicking all online CPUs.
*/
if (!cpumask_available(tmp))
return;
/*
* Note, the vCPU could get migrated to a different pCPU at any point
* after kvm_request_needs_ipi(), which could result in sending an IPI
* to the previous pCPU. But, that's OK because the purpose of the IPI
* is to ensure the vCPU returns to OUTSIDE_GUEST_MODE, which is
* satisfied if the vCPU migrates. Entering READING_SHADOW_PAGE_TABLES
* after this point is also OK, as the requirement is only that KVM wait
* for vCPUs that were reading SPTEs _before_ any changes were
* finalized. See kvm_vcpu_kick() for more details on handling requests.
*/
if (kvm_request_needs_ipi(vcpu, req)) {
cpu = READ_ONCE(vcpu->cpu);
if (cpu != -1 && cpu != current_cpu)
__cpumask_set_cpu(cpu, tmp);
}
}
bool kvm_make_vcpus_request_mask(struct kvm *kvm, unsigned int req,
struct kvm_vcpu *except,
unsigned long *vcpu_bitmap, cpumask_var_t tmp)
{
int i, cpu, me;
struct kvm_vcpu *vcpu;
int i, me;
bool called;
me = get_cpu();
kvm_for_each_vcpu(i, vcpu, kvm) {
if ((vcpu_bitmap && !test_bit(i, vcpu_bitmap)) ||
vcpu == except)
for_each_set_bit(i, vcpu_bitmap, KVM_MAX_VCPUS) {
vcpu = kvm_get_vcpu(kvm, i);
if (!vcpu || vcpu == except)
continue;
kvm_make_request(req, vcpu);
if (!(req & KVM_REQUEST_NO_WAKEUP) && kvm_vcpu_wake_up(vcpu))
continue;
/*
* tmp can be "unavailable" if cpumasks are allocated off stack
* as allocation of the mask is deliberately not fatal and is
* handled by falling back to kicking all online CPUs.
*/
if (!cpumask_available(tmp))
continue;
/*
* Note, the vCPU could get migrated to a different pCPU at any
* point after kvm_request_needs_ipi(), which could result in
* sending an IPI to the previous pCPU. But, that's ok because
* the purpose of the IPI is to ensure the vCPU returns to
* OUTSIDE_GUEST_MODE, which is satisfied if the vCPU migrates.
* Entering READING_SHADOW_PAGE_TABLES after this point is also
* ok, as the requirement is only that KVM wait for vCPUs that
* were reading SPTEs _before_ any changes were finalized. See
* kvm_vcpu_kick() for more details on handling requests.
*/
if (kvm_request_needs_ipi(vcpu, req)) {
cpu = READ_ONCE(vcpu->cpu);
if (cpu != -1 && cpu != me)
__cpumask_set_cpu(cpu, tmp);
}
kvm_make_vcpu_request(kvm, vcpu, req, tmp, me);
}
called = kvm_kick_many_cpus(tmp, !!(req & KVM_REQUEST_WAIT));
@ -306,12 +313,23 @@ bool kvm_make_vcpus_request_mask(struct kvm *kvm, unsigned int req,
bool kvm_make_all_cpus_request_except(struct kvm *kvm, unsigned int req,
struct kvm_vcpu *except)
{
struct kvm_vcpu *vcpu;
cpumask_var_t cpus;
bool called;
int i, me;
zalloc_cpumask_var(&cpus, GFP_ATOMIC);
called = kvm_make_vcpus_request_mask(kvm, req, except, NULL, cpus);
me = get_cpu();
kvm_for_each_vcpu(i, vcpu, kvm) {
if (vcpu == except)
continue;
kvm_make_vcpu_request(kvm, vcpu, req, cpus, me);
}
called = kvm_kick_many_cpus(cpus, !!(req & KVM_REQUEST_WAIT));
put_cpu();
free_cpumask_var(cpus);
return called;