Re: [PATCH V4 5/5] powerpc/kvm/stats: Implement existing and add new halt polling vcpu stats

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On Tue, Jul 19, 2016 at 1:12 AM, Suraj Jitindar Singh
<sjitindarsingh@xxxxxxxxx> wrote:
> vcpu stats are used to collect information about a vcpu which can be viewed
> in the debugfs. For example halt_attempted_poll and halt_successful_poll
> are used to keep track of the number of times the vcpu attempts to and
> successfully polls. These stats are currently not used on powerpc.
>
> Implement incrementation of the halt_attempted_poll and
> halt_successful_poll vcpu stats for powerpc. Since these stats are summed
> over all the vcpus for all running guests it doesn't matter which vcpu
> they are attributed to, thus we choose the current runner vcpu of the
> vcore.
>
> Also add new vcpu stats: halt_poll_success_ns, halt_poll_fail_ns and
> halt_wait_ns to be used to accumulate the total time spend polling
> successfully, polling unsuccessfully and waiting respectively, and
> halt_successful_wait to accumulate the number of times the vcpu waits.
> Given that halt_poll_success_ns, halt_poll_fail_ns and halt_wait_ns are
> expressed in nanoseconds it is necessary to represent these as 64-bit
> quantities, otherwise they would overflow after only about 4 seconds.
>
> Given that the total time spend either polling or waiting will be known and
> the number of times that each was done, it will be possible to determine
> the average poll and wait times. This will give the ability to tune the kvm
> module parameters based on the calculated average wait and poll times.
>
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>

Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>

>
> ---
> Change Log:
>
> V3 -> V4:
>         - Instead of accounting just wait and poll time, separate these
>           into successful_poll_time, failed_poll_time and wait_time.
> ---
>  arch/powerpc/include/asm/kvm_host.h |  4 ++++
>  arch/powerpc/kvm/book3s.c           |  4 ++++
>  arch/powerpc/kvm/book3s_hv.c        | 36 +++++++++++++++++++++++++++++++-----
>  3 files changed, 39 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index f6304c5..f15ffc0 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -114,8 +114,12 @@ struct kvm_vcpu_stat {
>         u64 emulated_inst_exits;
>         u64 dec_exits;
>         u64 ext_intr_exits;
> +       u64 halt_poll_success_ns;
> +       u64 halt_poll_fail_ns;
> +       u64 halt_wait_ns;
>         u64 halt_successful_poll;
>         u64 halt_attempted_poll;
> +       u64 halt_successful_wait;
>         u64 halt_poll_invalid;
>         u64 halt_wakeup;
>         u64 dbell_exits;
> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
> index 47018fc..71eb8f3 100644
> --- a/arch/powerpc/kvm/book3s.c
> +++ b/arch/powerpc/kvm/book3s.c
> @@ -52,8 +52,12 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
>         { "dec",         VCPU_STAT(dec_exits) },
>         { "ext_intr",    VCPU_STAT(ext_intr_exits) },
>         { "queue_intr",  VCPU_STAT(queue_intr) },
> +       { "halt_poll_success_ns",       VCPU_STAT(halt_poll_success_ns) },
> +       { "halt_poll_fail_ns",          VCPU_STAT(halt_poll_fail_ns) },
> +       { "halt_wait_ns",               VCPU_STAT(halt_wait_ns) },
>         { "halt_successful_poll", VCPU_STAT(halt_successful_poll), },
>         { "halt_attempted_poll", VCPU_STAT(halt_attempted_poll), },
> +       { "halt_successful_wait",       VCPU_STAT(halt_successful_wait) },
>         { "halt_poll_invalid", VCPU_STAT(halt_poll_invalid) },
>         { "halt_wakeup", VCPU_STAT(halt_wakeup) },
>         { "pf_storage",  VCPU_STAT(pf_storage) },
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index a9de1d4..81072f2 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -2679,15 +2679,16 @@ static int kvmppc_vcore_check_block(struct kvmppc_vcore *vc)
>   */
>  static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
>  {
> +       ktime_t cur, start_poll, start_wait;
>         int do_sleep = 1;
> -       ktime_t cur, start;
>         u64 block_ns;
>         DECLARE_SWAITQUEUE(wait);
>
>         /* Poll for pending exceptions and ceded state */
> -       cur = start = ktime_get();
> +       cur = start_poll = ktime_get();
>         if (vc->halt_poll_ns) {
> -               ktime_t stop = ktime_add_ns(start, vc->halt_poll_ns);
> +               ktime_t stop = ktime_add_ns(start_poll, vc->halt_poll_ns);
> +               ++vc->runner->stat.halt_attempted_poll;
>
>                 vc->vcore_state = VCORE_POLLING;
>                 spin_unlock(&vc->lock);
> @@ -2703,8 +2704,10 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
>                 spin_lock(&vc->lock);
>                 vc->vcore_state = VCORE_INACTIVE;
>
> -               if (!do_sleep)
> +               if (!do_sleep) {
> +                       ++vc->runner->stat.halt_successful_poll;
>                         goto out;
> +               }
>         }
>
>         prepare_to_swait(&vc->wq, &wait, TASK_INTERRUPTIBLE);
> @@ -2712,9 +2715,14 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
>         if (kvmppc_vcore_check_block(vc)) {
>                 finish_swait(&vc->wq, &wait);
>                 do_sleep = 0;
> +               /* If we polled, count this as a successful poll */
> +               if (vc->halt_poll_ns)
> +                       ++vc->runner->stat.halt_successful_poll;
>                 goto out;
>         }
>
> +       start_wait = ktime_get();
> +
>         vc->vcore_state = VCORE_SLEEPING;
>         trace_kvmppc_vcore_blocked(vc, 0);
>         spin_unlock(&vc->lock);
> @@ -2723,11 +2731,29 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
>         spin_lock(&vc->lock);
>         vc->vcore_state = VCORE_INACTIVE;
>         trace_kvmppc_vcore_blocked(vc, 1);
> +       ++vc->runner->stat.halt_successful_wait;
>
>         cur = ktime_get();
>
>  out:
> -       block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
> +       block_ns = ktime_to_ns(cur) - ktime_to_ns(start_poll);
> +
> +       /* Attribute wait time */
> +       if (do_sleep) {
> +               vc->runner->stat.halt_wait_ns +=
> +                       ktime_to_ns(cur) - ktime_to_ns(start_wait);
> +               /* Attribute failed poll time */
> +               if (vc->halt_poll_ns)
> +                       vc->runner->stat.halt_poll_fail_ns +=
> +                               ktime_to_ns(start_wait) -
> +                               ktime_to_ns(start_poll);
> +       } else {
> +               /* Attribute successful poll time */
> +               if (vc->halt_poll_ns)
> +                       vc->runner->stat.halt_poll_success_ns +=
> +                               ktime_to_ns(cur) -
> +                               ktime_to_ns(start_poll);
> +       }
>
>         /* Adjust poll time */
>         if (halt_poll_max_ns) {
> --
> 2.5.5
>
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