Dong, Eddie wrote: > > >> -----Original Message----- >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] >> Sent: 2007年10月23日 14:38 >> To: Dong, Eddie >> Cc: kvm-devel@lists.sourceforge.net >> Subject: Re: [kvm-devel] High vm-exit latencies during kvm >> boot-up/shutdown >> >> Dong, Eddie wrote: >>> [EMAIL PROTECTED] wrote: >>>> Hi, >>>> >>>> I'm seeing fairly high vm-exit latencies (300-400 us) >> during and only >>>> during qemu/kvm startup and shutdown on a Core2 T5500 in >> 32-bit mode. >>>> It's most probably while the VM runs inside bios code. >> During the rest >>>> of the time, while some Linux guest is running, the exit >> latencies are >>>> within microseconds, thus perfectly fine for the real-time scenarios >>>> I have in mind. >>> How is this time spent? All in Qemu? >> Most probably. I have a function tracer installed, and it does not >> report any kernel function call between the begin of the asm block and >> its end. > > If the time is spent in Qemu, then it is possible to be that long > since Qemu may read/write disk for the VM virtual disk.
Clarification: I can't precisely tell what code is executed in VM mode, as I don't have qemu or that guest instrumented. I just see the kernel entering VM mode and leaving it again more than 300 us later. So I wonder why this is allowed while some external IRQ is pending. > >>> Usually a kernel only VM Exit cost less than 1us. >> That's what I'm seeing for the rest as well. >> >> I have read that certain guest states do not allow preemptions by >> external interrupts (here it is the timer IRQ), but both >> GUEST_INTERRUPTIBILITY_INFO and GUEST_ACTIVITY_STATE are 0 on entry, >> e.g. Is there a way for the guest to trigger a non-preemptible SMM >> entry, and that without the kernel noticing it? >> > I am not aware of this possibility. > Eddie Jan
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