On 2013-02-21 09:43, 张智 wrote: > > > >> Date: Thu, 21 Feb 2013 08:39:40 +0100 >> From: jan.kis...@web.de >> To: zhangzhi2...@hotmail.com >> Subject: Re: kvm_external interrupt >> >> On 2013-02-21 06:49, zhang zhi wrote: >>> Hi Dear Jan, >>> >>> I have one question to ask : when I'm using the guest os to do some keyboard >>> input, I feel no time delay as if guest os were on the bare-metal machine. >> >> Your "measurement" can't reveal the existing delay. It's in the order of >> milliseconds, at most. >> > So regardless of ELI and posted interrupts, when user is using keyboard input > to interact with guest os, the keyboard event is still intercepted by vmm, > which handles the interrupt according to interrupt descriptor table of vmm. > After that, vmm finally delivers the corresponding interrupt to guest os > using inter-processor interrupt. > Is that so?
In general (independent of KVM), if the hypervisor has to share a device between different guests or between itself (in case of KVM, the Linux host is the hypervisor) and a guest, it has to intercept access to and events from that device. The PC keyboard is usually shared (and you can't allow a guest direct access to it as that I/O port can reset the host). So its interrupt is in first handled by the host and then potentially forwarded to a guest. That may happen via posted interrupts in the future or via event injection into the VCPU. If the physical interrupt triggered on a different CPU than the target VCPU is running on (and you don't have posted interrupts), you also need a host-side IPI to kick the VCPU out of guest mode, enabling the injection of the virtual interrupt on re-entry. HTH, Jan
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