Re: [PATCH 4/6] psi: introduce state_mask to represent stalled psi states

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Dec 14, 2018 at 09:15:06AM -0800, Suren Baghdasaryan wrote:
> The psi monitoring patches will need to determine the same states as
> record_times(). To avoid calculating them twice, maintain a state mask
> that can be consulted cheaply. Do this in a separate patch to keep the
> churn in the main feature patch at a minimum.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  include/linux/psi_types.h |  3 +++
>  kernel/sched/psi.c        | 29 +++++++++++++++++++----------
>  2 files changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
> index 2cf422db5d18..2c6e9b67b7eb 100644
> --- a/include/linux/psi_types.h
> +++ b/include/linux/psi_types.h
> @@ -53,6 +53,9 @@ struct psi_group_cpu {
>  	/* States of the tasks belonging to this group */
>  	unsigned int tasks[NR_PSI_TASK_COUNTS];
>  
> +	/* Aggregate pressure state derived from the tasks */
> +	u32 state_mask;
> +
>  	/* Period time sampling buckets for each state of interest (ns) */
>  	u32 times[NR_PSI_STATES];
>  

Since we spend so much time counting space in that line, maybe add a
note to the Changlog about how this fits.

Also, since I just had to re-count, you might want to add explicit
numbers to the psi_res and psi_states enums.

> +		if (state_mask & (1 << s))

We have the BIT() macro, but I'm honestly not sure that will improve
things.