Re: [RFC PATCH] psi: introduce PSI UNINTERRUPTIBLE

[Chengming Zhou]

On 2022/8/8 14:13, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> 
> Uninterruptible sleep has not been monitored as an important system status yet.
> Imagin that a set of psi triggers are created for monitoring a special group, while
> get nothing high for none of the pressures, which could be the processes within
> are stock in some given resources and turn to be UN status. Introduce PSI_UN as
> a sub-type among PSI system here.

Hello,

The problem is that not all TASK_UNINTERRUPTIBLE task means stalled on some
shared resource, like many schedule_timeout() paths.

Thanks.

> 
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
>  include/linux/psi_types.h | 11 ++++++++---
>  kernel/sched/psi.c        | 10 ++++++++++
>  kernel/sched/stats.h      |  6 +++++-
>  3 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
> index c7fe7c0..8cc1979 100644
> --- a/include/linux/psi_types.h
> +++ b/include/linux/psi_types.h
> @@ -15,6 +15,7 @@ enum psi_task_count {
>  	NR_IOWAIT,
>  	NR_MEMSTALL,
>  	NR_RUNNING,
> +	NR_UNINTERRUPTIBLE,
>  	/*
>  	 * This can't have values other than 0 or 1 and could be
>  	 * implemented as a bit flag. But for now we still have room
> @@ -32,7 +33,7 @@ enum psi_task_count {
>  	 * threads and memstall ones.
>  	 */
>  	NR_MEMSTALL_RUNNING,
> -	NR_PSI_TASK_COUNTS = 5,
> +	NR_PSI_TASK_COUNTS = 6,
>  };
>  
>  /* Task state bitmasks */
> @@ -41,13 +42,15 @@ enum psi_task_count {
>  #define TSK_RUNNING	(1 << NR_RUNNING)
>  #define TSK_ONCPU	(1 << NR_ONCPU)
>  #define TSK_MEMSTALL_RUNNING	(1 << NR_MEMSTALL_RUNNING)
> +#define TSK_UNINTERRUPTIBLE	(1 << NR_UNINTERRUPTIBLE)
>  
>  /* Resources that workloads could be stalled on */
>  enum psi_res {
>  	PSI_IO,
>  	PSI_MEM,
>  	PSI_CPU,
> -	NR_PSI_RESOURCES = 3,
> +	PSI_UN,
> +	NR_PSI_RESOURCES = 4,
>  };
>  
>  /*
> @@ -63,9 +66,11 @@ enum psi_states {
>  	PSI_MEM_FULL,
>  	PSI_CPU_SOME,
>  	PSI_CPU_FULL,
> +	PSI_UN_SOME,
> +	PSI_UN_FULL,
>  	/* Only per-CPU, to weigh the CPU in the global average: */
>  	PSI_NONIDLE,
> -	NR_PSI_STATES = 7,
> +	NR_PSI_STATES = 9,
>  };
>  
>  enum psi_aggregators {
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index a337f3e..a37b4a4 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -231,6 +231,10 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
>  		return unlikely(tasks[NR_RUNNING] > tasks[NR_ONCPU]);
>  	case PSI_CPU_FULL:
>  		return unlikely(tasks[NR_RUNNING] && !tasks[NR_ONCPU]);
> +	case PSI_UN_SOME:
> +		return unlikely(tasks[NR_UNINTERRUPTIBLE]);
> +	case PSI_UN_FULL:
> +		return unlikely(tasks[NR_UNINTERRUPTIBLE] && !tasks[NR_RUNNING]);
>  	case PSI_NONIDLE:
>  		return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
>  			tasks[NR_RUNNING];
> @@ -683,6 +687,12 @@ static void record_times(struct psi_group_cpu *groupc, u64 now)
>  			groupc->times[PSI_CPU_FULL] += delta;
>  	}
>  
> +	if (groupc->state_mask & (1 << PSI_UN_SOME)) {
> +		groupc->times[PSI_UN_SOME] += delta;
> +		if (groupc->state_mask & (1 << PSI_UN_FULL))
> +			groupc->times[PSI_UN_FULL] += delta;
> +	}
> +
>  	if (groupc->state_mask & (1 << PSI_NONIDLE))
>  		groupc->times[PSI_NONIDLE] += delta;
>  }
> diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
> index baa839c..bf98829 100644
> --- a/kernel/sched/stats.h
> +++ b/kernel/sched/stats.h
> @@ -132,6 +132,7 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
>  		if (p->in_iowait)
>  			clear |= TSK_IOWAIT;
>  	}
> +	clear |= TSK_UNINTERRUPTIBLE;
>  
>  	psi_task_change(p, clear, set);
>  }
> @@ -139,6 +140,7 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
>  static inline void psi_dequeue(struct task_struct *p, bool sleep)
>  {
>  	int clear = TSK_RUNNING;
> +	int set = 0;
>  
>  	if (static_branch_likely(&psi_disabled))
>  		return;
> @@ -154,8 +156,10 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
>  
>  	if (p->in_memstall)
>  		clear |= (TSK_MEMSTALL | TSK_MEMSTALL_RUNNING);
> +	if (READ_ONCE(p->__state) & TASK_UNINTERRUPTIBLE)
> +		set = TSK_UNINTERRUPTIBLE;
>  
> -	psi_task_change(p, clear, 0);
> +	psi_task_change(p, clear, set);
>  }
>  
>  static inline void psi_ttwu_dequeue(struct task_struct *p)