On Sun, Nov 16, 2014 at 11:18:28PM +0100, Samuel Thibault wrote:
> Hello,
>
> Jan Kiszka, le Wed 12 Nov 2014 00:42:52 +0100, a écrit :
> > On 2014-11-11 19:55, Samuel Thibault wrote:
> > > jenkins.debian.net is running inside a KVM VM, and it runs nested
> > > KVM guests for its installation attempts. This goes fine with Linux
> > > kernels, but it is extremely slow with gnumach kernels.
>
> > You can try to catch a trace (ftrace) on the physical host.
> >
> > I suspect the setup forces a lot of instruction emulation, either on L0
> > or L1. And that is slower than QEMU is KVM does not optimize like QEMU does.
>
> Here is a sample of trace-cmd output dump: the same kind of pattern
> repeats over and over, with EXTERNAL_INTERRUPT happening mostly
> every other microsecond:
>
> qemu-system-x86-9752 [003] 4106.187755: kvm_exit: reason
> EXTERNAL_INTERRUPT rip 0xffffffffa02848b1 info 0 800000f6
> qemu-system-x86-9752 [003] 4106.187756: kvm_entry: vcpu 0
> qemu-system-x86-9752 [003] 4106.187757: kvm_exit: reason
> EXTERNAL_INTERRUPT rip 0xffffffffa02848b1 info 0 800000f6
> qemu-system-x86-9752 [003] 4106.187758: kvm_entry: vcpu 0
> qemu-system-x86-9752 [003] 4106.187759: kvm_exit: reason
> EXTERNAL_INTERRUPT rip 0xffffffffa02848b1 info 0 800000f6
> qemu-system-x86-9752 [003] 4106.187760: kvm_entry: vcpu 0
>
> The various functions being interrupted are vmx_vcpu_run
> (0xffffffffa02848b1 and 0xffffffffa0284972), handle_io
> (0xffffffffa027ee62), vmx_get_cpl (0xffffffffa027a7de),
> load_vmc12_host_state (0xffffffffa027ea31), native_read_tscp
> (0xffffffff81050a84), native_write_msr_safe (0xffffffff81050aa6),
> vmx_decache_cr0_guest_bits (0xffffffffa027a384),
> vmx_handle_external_intr (0xffffffffa027a54d).
>
> AIUI, the external interrupt is 0xf6, i.e. Linux' IRQ_WORK_VECTOR. I
> however don't see any of them, neither in L0's /proc/interrupts, nor in
> L1's /proc/interrupts...
>
Do you know how gnumach timekeeping works? Does it have a timer that fires each
1ms?
Which clock device is it using?
--
Gleb.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
