Dor Laor wrote: > On Wed, 2008-03-19 at 17:39 +0200, Avi Kivity wrote: > >> Anthony Liguori wrote: >> >>> Avi Kivity wrote: >>> >>>> The fourth is probably impossible from userspace (and very >>>> difficult in the kernel). >>>> >>> What makes it impossible to do in userspace? If you managed a >>> tsc_offset in userspace, you would of course need to adjust that >>> tsc_offset within the kernel for the particular PCPU that you were on. >>> >>> >> In the kernel you can to tricks like local_irq_disable(); rdtsc(); >> ktime_get(); local_irq_enable() to get a sense where the tsc is. >> > > but you can also do it before the vcpu goes to userspace after vmexit. > >
You only want to do it when needed. We might add an ioctl for it, but it's tricky. >> Take a look at kvm_inject_pit_timer_irqs() and >> kvm_pit_timer_intr_post(). An attempt to have a accurate userspace pit >> needs to take into account what those functions do. I believe it's >> doable, but will require careful design of the interface (which should >> be usable for rtc and hpet as well). >> >> > > Actually I'm coming to think we don't need a irq queue in the kernel. > We just need to count the pending timer interrupts in userspace and > change the qemu_set_irq interface to return a status when the irq was > really injected by pic/apic (like kvm_pit_timer_intr_post). > > This way qemu timer devices will not inject another irq until the > previous irq got ack by the kernel (or even userspace pic/acpi). > Yes, I think you're right. We can return the information in the vcpu shared area, so it doesn't generate new exits. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
