On Mon, Jun 1, 2015 at 6:17 PM, 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 start function and provide a ratio
> of
> sleep time to normal execution time.
>
> Signed-off-by: Jason J. Herne <jjhe...@linux.vnet.ibm.com>
> Reviewed-by: Matthew Rosato <mjros...@linux.vnet.ibm.com>
> ---
> cpus.c | 62
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/qom/cpu.h | 46 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 108 insertions(+)
>
> diff --git a/cpus.c b/cpus.c
> index de6469f..7568357 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -64,6 +64,9 @@
>
> #endif /* CONFIG_LINUX */
>
> +/* Number of ms between cpu throttle operations */
> +#define CPU_THROTTLE_TIMESLICE 10
> +
> static CPUState *next_cpu;
> int64_t max_delay;
> int64_t max_advance;
> @@ -919,6 +922,65 @@ static void qemu_kvm_wait_io_event(CPUState *cpu)
> qemu_wait_io_event_common(cpu);
> }
>
> +static void cpu_throttle_thread(void *opq)
> +{
> + CPUState *cpu = (CPUState *)opq;
> + long sleeptime_ms = (long)(cpu->throttle_ratio * CPU_THROTTLE_TIMESLICE);
> +
> + /* Stop the timer if needed */
> + if (cpu->throttle_timer_stop) {
> + timer_del(cpu->throttle_timer);
> + timer_free(cpu->throttle_timer);
> + cpu->throttle_timer = NULL;
> + return;
> + }
> +
> + qemu_mutex_unlock_iothread();
> + g_usleep(sleeptime_ms * 1000); /* Convert ms to us for usleep call */
> + qemu_mutex_lock_iothread();
> +
> + timer_mod(cpu->throttle_timer, qemu_clock_get_ms(QEMU_CLOCK_REALTIME) +
> + CPU_THROTTLE_TIMESLICE);
> +}
> +
> +static void cpu_throttle_timer_pop(void *opq)
> +{
> + CPUState *cpu = (CPUState *)opq;
> +
> + async_run_on_cpu(cpu, cpu_throttle_thread, cpu);
> +}
> +
> +void cpu_throttle_start(CPUState *cpu, float throttle_ratio)
> +{
> + assert(throttle_ratio > 0);
> + cpu->throttle_ratio = throttle_ratio;
> +
> + if (!cpu_throttle_active(cpu)) {
> + cpu->throttle_timer = timer_new_ms(QEMU_CLOCK_REALTIME,
> + cpu_throttle_timer_pop, cpu);
> + timer_mod(cpu->throttle_timer,
> qemu_clock_get_ms(QEMU_CLOCK_REALTIME) +
> + CPU_THROTTLE_TIMESLICE);
> + cpu->throttle_timer_stop = false;
> + }
> +}
> +
> +void cpu_throttle_stop(CPUState *cpu)
> +{
> + assert(cpu_throttle_active(cpu));
> + cpu->throttle_timer_stop = true;
> +}
> +
> +bool cpu_throttle_active(CPUState *cpu)
> +{
> + return (cpu->throttle_timer != NULL);
> +}
> +
> +float cpu_throttle_get_ratio(CPUState *cpu)
> +{
> + assert(cpu_throttle_active(cpu));
> + return cpu->throttle_ratio;
> +}
> +
> static void *qemu_kvm_cpu_thread_fn(void *arg)
> {
> CPUState *cpu = arg;
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 39f0f19..9d16e6a 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -310,6 +310,11 @@ struct CPUState {
> uint32_t can_do_io;
> int32_t exception_index; /* used by m68k TCG */
>
> + /* vcpu throttling controls */
> + QEMUTimer *throttle_timer;
> + bool throttle_timer_stop;
> + float throttle_ratio;
> +
> /* Note that this is accessed at the start of every TB via a negative
> offset from AREG0. Leave this field at the end so as to make the
> (absolute value) offset as small as possible. This reduces code
> @@ -553,6 +558,47 @@ CPUState *qemu_get_cpu(int index);
> */
> bool cpu_exists(int64_t id);
>
> +/**
> + * cpu_throttle_start:
> + * @cpu: The vcpu to throttle
> + *
> + * Throttles a vcpu by forcing it to sleep. The duration of the sleep is a
> + * ratio of sleep time to running time. A ratio of 1.0 corresponds to a 50%
> + * duty cycle (example: 10ms sleep for every 10ms awake).
> + *
> + * cpu_throttle_start can be called as needed to adjust the throttle ratio.
> + * Once the throttling starts, it will remain in effect until
> cpu_throttle_stop
> + * is called.
> + */
> +void cpu_throttle_start(CPUState *cpu, float throttle_ratio);
> +
> +/**
> + * cpu_throttle_stop:
> + * @cpu: The vcpu to stop throttling
> + *
> + * Stops the vcpu throttling started by cpu_throttle_start.
> + */
> +void cpu_throttle_stop(CPUState *cpu);
> +
> +/**
> + * cpu_throttle_active:
> + * @cpu: The vcpu to check
> + *
> + * Returns %true if this vcpu is currently being throttled, %false otherwise.
> + */
> +bool cpu_throttle_active(CPUState *cpu);
> +
> +/**
> + * cpu_throttle_get_ratio:
> + * @cpu: The vcpu whose throttle ratio to return.
> + *
> + * Returns the ratio being used to throttle this vcpu. See cpu_throttle_start
> + * for details.
> + *
> + * Returns The ratio being used to throttle this vcpu.
> + */
> +float cpu_throttle_get_ratio(CPUState *cpu);
> +
> #ifndef CONFIG_USER_ONLY
>
> typedef void (*CPUInterruptHandler)(CPUState *, int);
> --
> 1.9.1
>
>
Thanks Jason, this patch would be quite interesting as it eliminates
slight overhead from scheduler when cgroups are actively used for same
task (~5% for per-vcpu cgroup layout simular to libvirt`s one for
guest perf numa bench). Are you planning to add wakeup frequency
throttler as well to same interface?
