| Message ID | 20170821203530.9266-7-rkrcmar@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 21.08.2017 22:35, Radim Krčmář wrote: > 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.) I think I prefer dropping this patch and maybe _after_ we have the list implementation in place, simply start walking the list from last_boosted_vcpu? (store a pointer instead of an index then, of course) If I understand correctly, this would then be simply, one walk from last_boosted_vcpu until we hit last_boosted_vcpu again. > > Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> > --- > 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); > >
On Tue, 22 Aug 2017 16:06:57 +0200 David Hildenbrand <david@redhat.com> wrote: > On 21.08.2017 22:35, Radim Krčmář wrote: > > 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.) > > I think I prefer dropping this patch and maybe _after_ we have the list > implementation in place, simply start walking the list from > last_boosted_vcpu? (store a pointer instead of an index then, of course) > > If I understand correctly, this would then be simply, one walk from > last_boosted_vcpu until we hit last_boosted_vcpu again. Yes, doing this change at this point in the series trades an ugly piece of code for a slightly less ugly one. > > > > Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> > > --- > > 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); \ > > + })) The loop below is better after the change, but this macro... it gets at least a bit better if you push this behind patch 8. > > + > > 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); > > > > > >
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);
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 <rkrcmar@redhat.com> --- include/linux/kvm_host.h | 13 +++++++++++++ virt/kvm/kvm_main.c | 47 ++++++++++++++++++----------------------------- 2 files changed, 31 insertions(+), 29 deletions(-)