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. > > 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). ------------------------------------------------------------------------- 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
