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... Samuel
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