On 2014-11-16 23:18, 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 You may want to turn on more trace events, if not all, to possibly see what Linux does then. The next level after that is function tracing (may require a kernel rebuild or a tracing kernel of the distro). > > 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... I suppose this is a SMP host and guest? Does reducing CPUs to 1 change to picture? If not, it may help to understand cause and effect easier. Jan
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