Commit 2adcc85d authored by Jason J. Herne's avatar Jason J. Herne Committed by Juan Quintela
Browse files

cpu: Provide vcpu throttling interface 



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: default avatarJason J. Herne <jjherne@linux.vnet.ibm.com>
Reviewed-by: default avatarMatthew Rosato <mjrosato@linux.vnet.ibm.com>
Signed-off-by: default avatarJuan Quintela <quintela@redhat.com>
Reviewed-by: default avatarJuan Quintela <quintela@redhat.com>
parent 2a6e6e59

cpus.c

+78 −0
Original line number Diff line number Diff line
@@ -69,6 +69,14 @@ 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();
@@ -505,10 +513,80 @@ 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()) {

        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();

}



static void cpu_throttle_timer_tick(void *opaque)

{

    CPUState *cpu;

    double pct;



    /* Stop the timer if needed */

    if (!cpu_throttle_get_percentage()) {

        return;

    }

    CPU_FOREACH(cpu) {

        if (!atomic_xchg(&cpu->throttle_thread_scheduled, 1)) {

            async_run_on_cpu(cpu, cpu_throttle_thread, cpu);

        }

    }



    pct = (double)cpu_throttle_get_percentage()/100;

    timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +

                                   CPU_THROTTLE_TIMESLICE_NS / (1-pct));

}



void cpu_throttle_set(int new_throttle_pct)

{

    /* Ensure throttle percentage is within valid range */

    new_throttle_pct = MIN(new_throttle_pct, CPU_THROTTLE_PCT_MAX);

    new_throttle_pct = MAX(new_throttle_pct, CPU_THROTTLE_PCT_MIN);



    atomic_set(&throttle_percentage, new_throttle_pct);



    timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +

                                       CPU_THROTTLE_TIMESLICE_NS);

}



void cpu_throttle_stop(void)

{

    atomic_set(&throttle_percentage, 0);

}



bool cpu_throttle_active(void)

{

    return (cpu_throttle_get_percentage() != 0);

}



int cpu_throttle_get_percentage(void)

{

    return atomic_read(&throttle_percentage);

}



void cpu_ticks_init(void)

{

    seqlock_init(&timers_state.vm_clock_seqlock, NULL);

    vmstate_register(NULL, 0, &vmstate_timers, &timers_state);

    throttle_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,

                                           cpu_throttle_timer_tick, NULL);

}



void configure_icount(QemuOpts *opts, Error **errp)

include/qom/cpu.h

+42 −0
Original line number Diff line number Diff line
@@ -321,6 +321,11 @@ struct CPUState { 
    uint32_t can_do_io;

    int32_t exception_index; /* used by m68k TCG */



    /* Used to keep track of an outstanding cpu throttle thread for migration

     * autoconverge

     */

    bool throttle_thread_scheduled;



    /* 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
@@ -565,6 +570,43 @@ CPUState *qemu_get_cpu(int index); 
 */

bool cpu_exists(int64_t id);



/**

 * cpu_throttle_set:

 * @new_throttle_pct: Percent of sleep time. Valid range is 1 to 99.

 *

 * Throttles all vcpus by forcing them to sleep for the given percentage of

 * time. A throttle_percentage of 25 corresponds to a 75% duty cycle roughly.

 * (example: 10ms sleep for every 30ms awake).

 *

 * cpu_throttle_set can be called as needed to adjust new_throttle_pct.

 * Once the throttling starts, it will remain in effect until cpu_throttle_stop

 * is called.

 */

void cpu_throttle_set(int new_throttle_pct);



/**

 * cpu_throttle_stop:

 *

 * Stops the vcpu throttling started by cpu_throttle_set.

 */

void cpu_throttle_stop(void);



/**

 * cpu_throttle_active:

 *

 * Returns: %true if the vcpus are currently being throttled, %false otherwise.

 */

bool cpu_throttle_active(void);



/**

 * cpu_throttle_get_percentage:

 *

 * Returns the vcpu throttle percentage. See cpu_throttle_set for details.

 *

 * Returns: The throttle percentage in range 1 to 99.

 */

int cpu_throttle_get_percentage(void);



#ifndef CONFIG_USER_ONLY



typedef void (*CPUInterruptHandler)(CPUState *, int);