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    SubjectRe: [patch 0/3] kvm tool: Serial emulation overhaul

    btw., i just noticed another performance weirdness, running the
    latest version on -tip with such a 64-bit x86 kernel:

    make defconfig
    make kvmconfig # sidenote: sigh - this still needs a 'make oldconfig'


    and do a 'kvm run' into a shell, then I get a permanently busy
    kvm executable sucking up CPU time:

    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    28206 mingo 20 0 3586m 80m 1080 S 56.1 0.7 0:13.83 kvm
    29462 mingo 20 0 15380 1392 900 R 0.3 0.0 0:00.02 top

    perf kvm top suggests simple idling around of 16 CPUs:

    --------------------------------------------------------------------------------------------------
    PerfTop: 1635 irqs/sec kernel:91.1% us: 0.3% guest kernel: 8.5% guest us: 0.0% exact: 0.0% [1000Hz cycles], (all, 16 CPUs)
    --------------------------------------------------------------------------------------------------
    samples pcnt function DSO
    _______ _____ _________________________ _______________________________
    155.00 17.9% apic_timer_interrupt /home/mingo/linux/linux/vmlinux
    89.00 10.3% find_busiest_group /home/mingo/linux/linux/vmlinux
    66.00 7.6% native_apic_mem_write /home/mingo/linux/linux/vmlinux
    51.00 5.9% idle_cpu /home/mingo/linux/linux/vmlinux
    29.00 3.3% __rcu_pending /home/mingo/linux/linux/vmlinux
    25.00 2.9% run_posix_cpu_timers /home/mingo/linux/linux/vmlinux
    24.00 2.8% _raw_spin_lock /home/mingo/linux/linux/vmlinux
    19.00 2.2% cpumask_next_and /home/mingo/linux/linux/vmlinux
    19.00 2.2% ktime_get /home/mingo/linux/linux/vmlinux
    18.00 2.1% run_timer_softirq /home/mingo/linux/linux/vmlinux
    16.00 1.8% run_rebalance_domains /home/mingo/linux/linux/vmlinux
    16.00 1.8% native_sched_clock /home/mingo/linux/linux/vmlinux
    15.00 1.7% rcu_exit_nohz /home/mingo/linux/linux/vmlinux
    14.00 1.6% tick_nohz_stop_sched_tick /home/mingo/linux/linux/vmlinux
    14.00 1.6% hrtimer_run_queues /home/mingo/linux/linux/vmlinux

    NO_HZ is set in the .config.

    Btw., 'perf kvm' is in need of some love: for example it is
    unable to pick up a vmlinux from the current directory and
    ./vmlinux does not work either, it needs
    /home/mingo/linux/linux/vmlinux specified explicitly - that
    sucks.

    Ideally perf could be taught to talk to the guest kvm process
    and get its vmlinux home position (even better: its guest
    kallsyms) from there - so if i typed 'perf kvm top' it would do
    the right thing all automagically. [ What a fantastc level of
    automation! ;-) ]

    Thanks,

    Ingo


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