"Jason J. Herne" <jjhe...@linux.vnet.ibm.com> wrote:
> Provide a method to throttle guest cpu execution. CPUState is augmented with
> timeout controls and throttle start/stop functions. To throttle the guest cpu
> the caller simply has to call the throttle set function and provide a
> percentage
> of throttle time.
>
> Signed-off-by: Jason J. Herne <jjhe...@linux.vnet.ibm.com>
> Reviewed-by: Matthew Rosato <mjros...@linux.vnet.ibm.com>
> ---
> cpus.c | 78
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/qom/cpu.h | 42 ++++++++++++++++++++++++++++++
> 2 files changed, 120 insertions(+)
>
> diff --git a/cpus.c b/cpus.c
> index de6469f..b5ff9c9 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -68,6 +68,14 @@ static CPUState *next_cpu;
> int64_t max_delay;
> int64_t max_advance;
>
> +/* vcpu throttling controls */
> +static QEMUTimer *throttle_timer;
> +static unsigned int throttle_percentage;
> +
> +#define CPU_THROTTLE_PCT_MIN 1
> +#define CPU_THROTTLE_PCT_MAX 99
> +#define CPU_THROTTLE_TIMESLICE_NS 10000000
> +
> bool cpu_is_stopped(CPUState *cpu)
> {
> return cpu->stopped || !runstate_is_running();
> @@ -486,10 +494,80 @@ static const VMStateDescription vmstate_timers = {
> }
> };
>
> +static void cpu_throttle_thread(void *opaque)
> +{
> + CPUState *cpu = opaque;
> + double pct;
> + double throttle_ratio;
> + long sleeptime_ns;
> +
> + if (!cpu_throttle_get_percentage()) {
cpu_throotle_active()?
> + return;
> + }
> +
> + pct = (double)cpu_throttle_get_percentage()/100;
> + throttle_ratio = pct / (1 - pct);
> + sleeptime_ns = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS);
> +
> + qemu_mutex_unlock_iothread();
> + atomic_set(&cpu->throttle_thread_scheduled, 0);
> + g_usleep(sleeptime_ns / 1000); /* Convert ns to us for usleep call */
> + qemu_mutex_lock_iothread();
Why is this thread safe?
qemu_mutex_lock_iothread() is protecting (at least) cpu_work_first on
each cpu. How can we be sure that _nothing_ will change that while we
are waiting? A fast look through the tree don't show anything that
runs here that drops the lock. I am missing something?
> +}
> +
> +static void cpu_throttle_timer_tick(void *opaque)
> +{
> + CPUState *cpu;
> + double pct;
> +
> + /* Stop the timer if needed */
> + if (!cpu_throttle_get_percentage()) {
cpu_throotle_active()?
agree with rest of the changes.
Later, Juan.
