On Mon, 23 Jul 2012 16:14:02 +0300 Avi Kivity <avi@xxxxxxxxxx> wrote: > On 07/23/2012 04:06 PM, Cornelia Huck wrote: > > On Mon, 23 Jul 2012 15:18:49 +0300 > > Avi Kivity <avi@xxxxxxxxxx> wrote: > > > >> > So, for example, if a specific subchannel (=device) has pending status > >> > and an I/O interrupt is to be generated, this interrupt remains pending > >> > until an arbitrary cpu is enabled for I/O interrupts. If several cpus > >> > are enabled for I/O interrupts, any of them may be interrupted. > >> > >> This may be costly to emulate. On x86 we do not have access to a > >> guest's interrupt status while it is running. Is this not the case for > >> s390? > >> > >> Oh, let me guess. You write some interrupt descriptor in memory > >> somewhere, issue one of your famous instructions, and the hardware finds > >> a guest vcpu and injects the interrupt. > > > > Basically, we have some flags in our control block we can set so that > > the cpu drops out of SIE whenever external/I/O/... interrupts are > > enabled and then have the host do the lowcore updates, psw swaps, etc. > > Can you write them from a different cpu and expect them to take effect? > > How do you emulate an interrupt with a large guest? You have to update > the flags in the control blocks for all vcpus; then restore them when > the interrupt is delivered? We may access the flags for any vcpu via the kvm_s390_float_interrupt structure which is contained in kvm->arch. We'll get control when a vcpu enters a wait state and try to deliver pending interrupts or set/clear the flags. Moreover, idle vcpus are on a wait queue and are the first target for getting an interrupt injected. > >> While you don't have an irqchip, you do have asynchronous interrupt > >> injection, yes? That's what irqchip really is all about. > > > > You mean injection via ioctl() that is asynchronous to vcpu execution? > > Yes, although we use a different ioctl than the others. > > Ok. The difference between irqfd and the ioctl is that with irqfd > everything (the payload in your case, the interrupt number for others) > is prepared beforehand, while with the ioctl the extra information is > delivered with the ioctl. This should work for us. Cornelia -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
