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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 17 Dec 2018 16:55:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     gregkh@...uxfoundation.org, tj@...nel.org, lizefan@...wei.com,
        hannes@...xchg.org, axboe@...nel.dk, dennis@...nel.org,
        dennisszhou@...il.com, mingo@...hat.com, akpm@...ux-foundation.org,
        corbet@....net, cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH 4/6] psi: introduce state_mask to represent stalled psi
 states

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@...gle.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.