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

Peter Zijlstra
2018-12-17T15:55:42Z

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.