Re: [PATCH v2 3/4] kvm: Introduce a dirty rate calculation method based on dirty ring

[Hyman Huang]

在 2022/3/28 9:32, wucy11@chinatelecom.cn 写道:
> From: Chongyun Wu <wucy11@chinatelecom.cn>
>
> A new structure KVMDirtyRingDirtyCounter is introduced in
> KVMDirtyRingReaper to record the number of dirty pages
> within a period of time.
>
> When kvm_dirty_ring_mark_page collects dirty pages, if it
> finds that the current dirty pages are not duplicates, it
> increases the dirty_pages_period count.
>
> Divide the dirty_pages_period count by the interval to get
> the dirty page rate for this period.
>
> And use dirty_pages_period_peak_rate to count the highest
> dirty page rate, to solve the problem that the dirty page
> collection rate may change greatly during a period of time,
> resulting in a large change in the dirty page rate.
>
> Through sufficient testing, it is found that the dirty rate
> calculated after kvm_dirty_ring_flush usually matches the actual
> pressure, and the dirty rate counted per second may change in the
> subsequent seconds, so record the peak dirty rate as the real
> dirty pages rate.
>
> This dirty pages rate is mainly used as the subsequent autoconverge
> calculation speed limit throttle.
As Peter's advice, i think the better way is exporting or adapting the 
existing implemenation of dirty page rate calculation instead of 
building different blocks.
> Signed-off-by: Chongyun Wu <wucy11@chinatelecom.cn>
> ---
>   accel/kvm/kvm-all.c  | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>   include/sysemu/kvm.h |  2 ++
>   2 files changed, 65 insertions(+), 1 deletion(-)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 5e02700..a158b1c 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -114,6 +114,13 @@ enum KVMDirtyRingReaperSpeedControl {
>       KVM_DIRTY_RING_REAPER_SPEED_CONTROL_DOWN
>   };
>   
> +struct KVMDirtyRingDirtyCounter {
> +    int64_t time_last_count;
> +    uint64_t dirty_pages_period;
> +    int64_t dirty_pages_rate;
> +    int64_t dirty_pages_period_peak_rate;
> +};
> +
>   /*
>    * KVM reaper instance, responsible for collecting the KVM dirty bits
>    * via the dirty ring.
> @@ -128,6 +135,7 @@ struct KVMDirtyRingReaper {
>       uint64_t ring_full_cnt;
>       float ratio_adjust_threshold;
>       int stable_count_threshold;
> +    struct KVMDirtyRingDirtyCounter counter; /* Calculate dirty pages rate */
>   };
>   
>   struct KVMState
> @@ -739,7 +747,9 @@ static void kvm_dirty_ring_mark_page(KVMState *s, uint32_t 
> as_id,
>           return;
>       }
>   
> -    set_bit(offset, mem->dirty_bmap);
> +    if (!test_and_set_bit(offset, mem->dirty_bmap)) {
> +        s->reaper.counter.dirty_pages_period++;
> +    }
>   }
>   
>   static bool dirty_gfn_is_dirtied(struct kvm_dirty_gfn *gfn)
> @@ -783,6 +793,56 @@ static uint32_t kvm_dirty_ring_reap_one(KVMState *s, 
> CPUState *cpu)
>       return count;
>   }
>   
> +int64_t kvm_dirty_ring_get_rate(void)
> +{
> +    return kvm_state->reaper.counter.dirty_pages_rate;
> +}
> +
> +int64_t kvm_dirty_ring_get_peak_rate(void)
> +{
> +    return kvm_state->reaper.counter.dirty_pages_period_peak_rate;
> +}
> +
> +static void kvm_dirty_ring_reap_count(KVMState *s)
> +{
> +    int64_t spend_time = 0;
> +    int64_t end_time;
> +
> +    if (!s->reaper.counter.time_last_count) {
> +        s->reaper.counter.time_last_count =
> +            qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> +    }
> +
> +    end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> +    spend_time = end_time - s->reaper.counter.time_last_count;
> +
> +    if (!s->reaper.counter.dirty_pages_period ||
> +        !spend_time) {
> +        return;
> +    }
> +
> +    /*
> +     * More than 1 second = 1000 millisecons,
> +     * or trigger by kvm_log_sync_global which spend time
> +     * more than 300 milliscons.
> +     */
> +    if (spend_time > 1000) {
> +        /* Count the dirty page rate during this period */
> +        s->reaper.counter.dirty_pages_rate =
> +            s->reaper.counter.dirty_pages_period * 1000 / spend_time;
> +        /* Update the peak dirty page rate at this period */
> +        if (s->reaper.counter.dirty_pages_rate >
> +            s->reaper.counter.dirty_pages_period_peak_rate) {
> +            s->reaper.counter.dirty_pages_period_peak_rate =
> +                s->reaper.counter.dirty_pages_rate;
> +        }
> +
> +        /* Reset counters */
> +        s->reaper.counter.dirty_pages_period = 0;
> +        s->reaper.counter.time_last_count = 0;
> +    }
> +}
> +
>   /* Must be with slots_lock held */
>   static uint64_t kvm_dirty_ring_reap_locked(KVMState *s)
>   {
> @@ -793,6 +853,8 @@ static uint64_t kvm_dirty_ring_reap_locked(KVMState *s)
>   
>       stamp = get_clock();
>   
> +    kvm_dirty_ring_reap_count(s);
> +
>       CPU_FOREACH(cpu) {
>           total += kvm_dirty_ring_reap_one(s, cpu);
>       }
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index a783c78..05846f9 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -582,4 +582,6 @@ bool kvm_cpu_check_are_resettable(void);
>   bool kvm_arch_cpu_check_are_resettable(void);
>   
>   bool kvm_dirty_ring_enabled(void);
> +int64_t kvm_dirty_ring_get_rate(void);
> +int64_t kvm_dirty_ring_get_peak_rate(void);
>   #endif

--
Best regard

Hyman Huang(黄勇)