On 04/24/2012 03:55 PM, Christian Borntraeger wrote: > From: Konstantin Weitz <[email protected]> > > This patch implements the directed yield hypercall found on other > System z hypervisors. It delegates execution time to the virtual cpu > specified in the instruction's parameter. > > Useful to avoid long spinlock waits in the guest. > > > struct kvm_s390_io_info { > diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c > index a353f0e..022962b 100644 > --- a/arch/s390/kvm/diag.c > +++ b/arch/s390/kvm/diag.c > @@ -53,6 +53,45 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu) > return 0; > } > > +static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) > +{ > + struct kvm *kvm = vcpu->kvm; > + struct kvm_vcpu *tcpu; > + int tid; > + int i; > + > + tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4]; > + vcpu->stat.diagnose_9c++; > + VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d", tid); > + > + if (tid == vcpu->vcpu_id) > + return 0; > + > + kvm_for_each_vcpu(i, tcpu, kvm) { > + if (tcpu->vcpu_id == tid) { > + struct task_struct *task = NULL; > + struct pid *pid; > + rcu_read_lock(); > + pid = rcu_dereference(tcpu->pid); > + if (pid) > + task = get_pid_task(tcpu->pid, PIDTYPE_PID); > + rcu_read_unlock(); > + if (!task) > + break; > + if (task->flags & PF_VCPU) { > + put_task_struct(task); > + break; > + } > + if (yield_to(task, 1)) { > + put_task_struct(task); > + return 0; > + } > + put_task_struct(task); > + } > + } > + return 0; > +} > + >
I think the code will me more readable, and less obvious that is was copied from kvm_vcpu_on_spin(), if you put all the processing outside the loop, except for matching the vpu itself. So the code reads find a vcpu obtain the task do the yield instead of looking like you're doing the processing for every vcpu. The loop is just a slow lookup which might some day be replaced by a table lookup. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
