Re: [Xen-devel] [RFC 1/9] schedule: Introduce per-pcpu time accounting

[Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>]

Andrii,

Andrii Anisov writes:

> From: Andrii Anisov <andrii_anisov@xxxxxxxx>
>
> Introduce per-pcpu time accounting what includes the following states:
>
> TACC_HYP - the pcpu executes hypervisor code like softirq processing
>            (including scheduling), tasklets and context switches
> TACC_GUEST - the pcpu executes guests code
> TACC_IDLE - the low-power state of the pcpu
Is it really low-power?

> TACC_IRQ - the pcpu performs interrupts processing, without separation to
>            guest or hypervisor interrupts
I think, word "distinguishing" would be better than "separation"

> TACC_GSYNC - the pcpu executes hypervisor code to process synchronous trap
>              from the guest. E.g. hypercall processing or io emulation.
>
> Currently, the only reenterant state is TACC_IRQ. It is assumed, no changes
> to state other than TACC_IRQ could happen until we return from nested
> interrupts. IRQ time is accounted in a distinct way comparing to other states.
> It is acumulated between other states transition moments, and is substracted
> from the old state on states transion calculation.
>
> Signed-off-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
> ---
>  xen/common/schedule.c   | 81 
> +++++++++++++++++++++++++++++++++++++++++++++++++
>  xen/include/xen/sched.h | 27 +++++++++++++++++
>  2 files changed, 108 insertions(+)
>
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index 7b71581..6dd6603 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -1539,6 +1539,87 @@ static void schedule(void)
>      context_switch(prev, next);
>  }
>  
> +DEFINE_PER_CPU(struct tacc, tacc);
> +
> +static void tacc_state_change(enum TACC_STATES new_state)
> +{
> +    s_time_t now, delta;
> +    struct tacc* tacc = &this_cpu(tacc);
> +    unsigned long flags;
> +
> +    local_irq_save(flags);
> +
> +    now = NOW();
> +    delta = now - tacc->state_entry_time;
> +
> +    /* We do not expect states reenterability (at least through this 
> function)*/
> +    ASSERT(new_state != tacc->state);
> +
> +    tacc->state_time[tacc->state] += delta - tacc->irq_time;
> +    tacc->state_time[TACC_IRQ] += tacc->irq_time;
> +    tacc->irq_time = 0;
> +    tacc->state = new_state;
> +    tacc->state_entry_time = now;
> +
> +    local_irq_restore(flags);
> +}
> +
> +void tacc_hyp(int place)
I believe, you want some enum for this "place" parameter type
> +{
> +//    printk("\ttacc_hyp %u, place %d\n", smp_processor_id(), place);
Please, don't push commented-out code. BTW, I think, it is possible to
add some TACC_DEBUG facilities to enable/disable this traces during
compile-time.

Also, looks like you don't use "place" parameter at all.

Lastly, I believe that this function (and other similar functions below)
can be defined as "static inline" in a header file.

> +    tacc_state_change(TACC_HYP);
> +}
> +
> +void tacc_guest(int place)
> +{
> +//    printk("\ttacc_guest %u, place %d\n", smp_processor_id(), place);
> +    tacc_state_change(TACC_GUEST);
> +}
> +
> +void tacc_idle(int place)
> +{
> +//    printk("\tidle cpu %u, place %d\n", smp_processor_id(), place);
> +    tacc_state_change(TACC_IDLE);
> +}
> +
> +void tacc_gsync(int place)
> +{
> +//    printk("\ttacc_gsync %u, place %d\n", smp_processor_id(), place);
> +    tacc_state_change(TACC_GSYNC);
> +}
> +
> +void tacc_irq_enter(int place)
> +{
> +    struct tacc* tacc = &this_cpu(tacc);
> +
> +//    printk("\ttacc_irq_enter %u, place %d, cnt %d\n", smp_processor_id(), 
> place, this_cpu(tacc).irq_cnt);
> +    ASSERT(!local_irq_is_enabled());
> +    ASSERT(tacc->irq_cnt >= 0);
You can make irq_cnt unsigned and drop this assert.

> +
> +    if ( tacc->irq_cnt == 0 )
> +    {
> +        tacc->irq_enter_time = NOW();
> +    }
Coding style:

---
Braces should be omitted for blocks with a single statement. e.g.,

if ( condition )
    single_statement();
---

> +
> +    tacc->irq_cnt++;
> +}
> +
> +void tacc_irq_exit(int place)
> +{
> +    struct tacc* tacc = &this_cpu(tacc);
> +
> +//    printk("\ttacc_irq_exit %u, place %d, cnt %d\n", smp_processor_id(), 
> place, tacc->irq_cnt);
> +    ASSERT(!local_irq_is_enabled());
> +    ASSERT(tacc->irq_cnt > 0);
> +    if ( tacc->irq_cnt == 1 )
> +    {
> +        tacc->irq_time = NOW() - tacc->irq_enter_time;
> +        tacc->irq_enter_time = 0;
> +    }
> +
> +    tacc->irq_cnt--;
What if, you IRQ will arrive right after this? I believe, you will lose
some of the accumulated time.

> +}
> +
>  void context_saved(struct vcpu *prev)
>  {
>      /* Clear running flag /after/ writing context to memory. */
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index e3601c1..04a8724 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -1002,6 +1002,33 @@ extern void dump_runq(unsigned char key);
>  
>  void arch_do_physinfo(struct xen_sysctl_physinfo *pi);
>  
> +enum TACC_STATES {
If I remember correct, enum names should in lower case

> +    TACC_HYP = 0,
> +    TACC_GUEST = 1,
> +    TACC_IDLE = 2,
> +    TACC_IRQ = 3,
> +    TACC_GSYNC = 4,
> +    TACC_STATES_MAX
> +};
> +
> +struct tacc
> +{
> +    s_time_t state_time[TACC_STATES_MAX];
> +    s_time_t state_entry_time;
> +    int state;
enum, maybe?

> +
> +    s_time_t guest_time;
> +
> +    s_time_t irq_enter_time;
> +    s_time_t irq_time;
> +    int irq_cnt;
> +};
> +
> +DECLARE_PER_CPU(struct tacc, tacc);
> +
> +void tacc_hyp(int place);
> +void tacc_idle(int place);
What about functions from sched.c? Should they be declared there?

> +
>  #endif /* __SCHED_H__ */
>  
>  /*


-- 
Volodymyr Babchuk at EPAM
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