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    Subject[PATCH v2 5/7] KVM-GST: KVM Steal time accounting
    Date
    This patch accounts steal time time in kernel/sched.
    I kept it from last proposal, because I still see advantages
    in it: Doing it here will give us easier access from scheduler
    variables such as the cpu rq. The next patch shows an example of
    usage for it.

    Since functions like account_idle_time() can be called from
    multiple places, not only account_process_tick(), steal time
    grabbing is repeated in each account function separatedely.

    Signed-off-by: Glauber Costa <glommer@redhat.com>
    CC: Rik van Riel <riel@redhat.com>
    CC: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    CC: Peter Zijlstra <peterz@infradead.org>
    CC: Avi Kivity <avi@redhat.com>
    CC: Anthony Liguori <aliguori@us.ibm.com>
    CC: Eric B Munson <emunson@mgebm.net>
    ---
    kernel/sched.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
    1 files changed, 53 insertions(+), 0 deletions(-)

    diff --git a/kernel/sched.c b/kernel/sched.c
    index 3f2e502..fa983c6 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -75,6 +75,7 @@
    #include <asm/tlb.h>
    #include <asm/irq_regs.h>
    #include <asm/mutex.h>
    +#include <asm/paravirt.h>

    #include "sched_cpupri.h"
    #include "workqueue_sched.h"
    @@ -528,6 +529,7 @@ struct rq {
    #ifdef CONFIG_IRQ_TIME_ACCOUNTING
    u64 prev_irq_time;
    #endif
    + u64 prev_steal_time;

    /* calc_load related fields */
    unsigned long calc_load_update;
    @@ -3705,6 +3707,49 @@ unsigned long long thread_group_sched_runtime(struct task_struct *p)
    }

    /*
    + * We have to at flush steal time information every time something else
    + * is accounted. Since the accounting functions are all visible to the rest
    + * of the kernel, it gets tricky to do them in one place. This helper function
    + * helps us.
    + *
    + * When the system is idle, the concept of steal time does not apply. We just
    + * tell the underlying hypervisor that we grabbed the data, but skip steal time
    + * accounting
    + */
    +static inline bool touch_steal_time(int is_idle)
    +{
    + u64 steal, st = 0;
    +
    + if (static_branch(&paravirt_steal_enabled)) {
    +
    + steal = paravirt_steal_clock(smp_processor_id());
    +
    + steal -= this_rq()->prev_steal_time;
    + if (is_idle) {
    + this_rq()->prev_steal_time += steal;
    + return false;
    + }
    +
    + while (steal >= TICK_NSEC) {
    + /*
    + * Inline assembly required to prevent the compiler
    + * optimising this loop into a divmod call.
    + * See __iter_div_u64_rem() for another example of this.
    + */
    + asm("" : "+rm" (steal));
    +
    + steal -= TICK_NSEC;
    + this_rq()->prev_steal_time += TICK_NSEC;
    + st++;
    + }
    +
    + account_steal_time(st);
    + return !!st;
    + }
    + return false;
    +}
    +
    +/*
    * Account user cpu time to a process.
    * @p: the process that the cpu time gets accounted to
    * @cputime: the cpu time spent in user space since the last update
    @@ -3716,6 +3761,9 @@ void account_user_time(struct task_struct *p, cputime_t cputime,
    struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
    cputime64_t tmp;

    + if (touch_steal_time(0))
    + return;
    +
    /* Add user time to process. */
    p->utime = cputime_add(p->utime, cputime);
    p->utimescaled = cputime_add(p->utimescaled, cputime_scaled);
    @@ -3802,6 +3850,9 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
    struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
    cputime64_t *target_cputime64;

    + if (touch_steal_time(0))
    + return;
    +
    if ((p->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) {
    account_guest_time(p, cputime, cputime_scaled);
    return;
    @@ -3839,6 +3890,8 @@ void account_idle_time(cputime_t cputime)
    cputime64_t cputime64 = cputime_to_cputime64(cputime);
    struct rq *rq = this_rq();

    + touch_steal_time(1);
    +
    if (atomic_read(&rq->nr_iowait) > 0)
    cpustat->iowait = cputime64_add(cpustat->iowait, cputime64);
    else
    --
    1.7.3.4


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