On Tue, Dec 1, 2009 at 10:17 AM, Jan Kiszka <jan.kis...@siemens.com> wrote: > Avi Kivity wrote: >> On 11/30/2009 07:30 PM, Jan Kiszka wrote: >>>>> No. But what's wrong with on_vcpu? >>>>> >>>> intrinsically racy. signal passing slow down things, etc. >>>> >>>> That said, as I've stated many times: I don't believe there's anything >>>> fundamentally wrong with on_vcpu. But we might get benefits from a >>>> re-design >>>> of things to avoid it whenever possible. (just like the vcpu_reset() >>>> I've just posted) >>>> >>>> >>> If you don't want immediate execution of update_guest_debug, save the >>> state that shall be transferred, set some flag, and run the transfer >>> before guest entry inside the vcpu threads (after putting the registers >>> as older kernels may otherwise overwrite the flags register). Should >>> work, may even avoid redundant calls during a gdb session. >>> >> >> There's no guarantee the vcpu will ever exit to qemu, so you have to >> signal the vcpu thread anyway. When you do that, you might as well load >> the new state. > > Debugging is special here as it involves vmstop before you start playing > with the debug settings. But I may also oversee some corner case right now. >
I imagined so. In this case, it might be better to set a flag before vmstop, and then honor it on vcpu entry. I had this feeling that in most cases where we current signal the vcpu, the VM will be already stopped anyway, so we don't need to resignal. -- Glauber Costa. "Free as in Freedom" http://glommer.net "The less confident you are, the more serious you have to act."