Re: [RFC PATCH v1 4/6] xentop: collect IRQ and HYP time statistics.

[Jürgen Groß <jgross@xxxxxxxx>]

On 12.06.20 02:22, Volodymyr Babchuk wrote:
> As scheduler code now collects time spent in IRQ handlers and in
> do_softirq(), we can present those values to userspace tools like
> xentop, so system administrator can see how system behaves.
>
> We are updating counters only in sched_get_time_correction() function
> to minimize number of taken spinlocks. As atomic_t is 32 bit wide, it
> is not enough to store time with nanosecond precision. So we need to
> use 64 bit variables and protect them with spinlock.
>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> ---
>   xen/common/sched/core.c     | 17 +++++++++++++++++
>   xen/common/sysctl.c         |  1 +
>   xen/include/public/sysctl.h |  4 +++-
>   xen/include/xen/sched.h     |  2 ++
>   4 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
> index a7294ff5c3..ee6b1d9161 100644
> --- a/xen/common/sched/core.c
> +++ b/xen/common/sched/core.c
> @@ -95,6 +95,10 @@ static struct scheduler __read_mostly ops;
>   
>   static bool scheduler_active;
>   
> +static DEFINE_SPINLOCK(sched_stat_lock);
> +s_time_t sched_stat_irq_time;
> +s_time_t sched_stat_hyp_time;
> +
>   static void sched_set_affinity(
>       struct sched_unit *unit, const cpumask_t *hard, const cpumask_t *soft);
>   
> @@ -994,9 +998,22 @@ s_time_t sched_get_time_correction(struct sched_unit *u)
>               break;
>       }
>   
> +    spin_lock_irqsave(&sched_stat_lock, flags);
> +    sched_stat_irq_time += irq;
> +    sched_stat_hyp_time += hyp;
> +    spin_unlock_irqrestore(&sched_stat_lock, flags);
Please don't use a lock. Just use add_sized() instead which will add
atomically.

> +
>       return irq + hyp;
>   }
>   
> +void sched_get_time_stats(uint64_t *irq_time, uint64_t *hyp_time)
> +{
> +    unsigned long flags;
> +
> +    spin_lock_irqsave(&sched_stat_lock, flags);
> +    *irq_time = sched_stat_irq_time;
> +    *hyp_time = sched_stat_hyp_time;
> +    spin_unlock_irqrestore(&sched_stat_lock, flags);
read_atomic() will do the job without lock.

>   }
>   
>   /*
> diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c
> index 1c6a817476..00683bc93f 100644
> --- a/xen/common/sysctl.c
> +++ b/xen/common/sysctl.c
> @@ -270,6 +270,7 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) 
> u_sysctl)
>           pi->scrub_pages = 0;
>           pi->cpu_khz = cpu_khz;
>           pi->max_mfn = get_upper_mfn_bound();
> +        sched_get_time_stats(&pi->irq_time, &pi->hyp_time);
>           arch_do_physinfo(pi);
>           if ( iommu_enabled )
>           {
> diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
> index 3a08c512e8..f320144d40 100644
> --- a/xen/include/public/sysctl.h
> +++ b/xen/include/public/sysctl.h
> @@ -35,7 +35,7 @@
>   #include "domctl.h"
>   #include "physdev.h"
>   
> -#define XEN_SYSCTL_INTERFACE_VERSION 0x00000013
> +#define XEN_SYSCTL_INTERFACE_VERSION 0x00000014
>   
>   /*
>    * Read console content from Xen buffer ring.
> @@ -118,6 +118,8 @@ struct xen_sysctl_physinfo {
>       uint64_aligned_t scrub_pages;
>       uint64_aligned_t outstanding_pages;
>       uint64_aligned_t max_mfn; /* Largest possible MFN on this host */
> +    uint64_aligned_t irq_time;
> +    uint64_aligned_t hyp_time;
Would hypfs work, too? This would avoid the need for extending another
hypercall.


Juergen