linux-kernel - Re: [PATCH 7/7] docs: proc.rst: stat: Note the interrupt counter wrap-around

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Message-ID: <a3aa1c2e-fabe-8911-d3ad-555a39ba3234@infradead.org>
Date:   Fri, 10 Sep 2021 20:59:26 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Alexei Lozovsky <me@...mmy.net>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 7/7] docs: proc.rst: stat: Note the interrupt counter
 wrap-around

On 9/10/21 8:48 PM, Alexei Lozovsky wrote:
> Let's make wrap-around documented behavior so that userspace has no
> excuses for not handling it properly if they want accurate values.
> 
> Both "intr" and "softirq" counters (as well as many others, actually)
> can and will wrap-around, given enough time since boot.
> 
> Signed-off-by: Alexei Lozovsky <me@...mmy.net>
> ---
>   Documentation/filesystems/proc.rst | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 042c418f4090..06a0e3aa2e0e 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -1513,6 +1513,13 @@ interrupts serviced  including  unnumbered  architecture specific  interrupts;
>   each  subsequent column is the  total for that particular numbered interrupt.
>   Unnumbered interrupts are not shown, only summed into the total.
>   
> +.. note::
> +
> +   Interrupt counters on most platforms are 32-bit, including the total count.
> +   Depending on the system load, ths values will sooner or later wrap around.

                                     these

> +   If you want accurate accouting of the rate and *real* number of interrupts

                            accounting

> +   serviced, you should monitor the value closely and handle wrap-arounds.
> +
>   The "ctxt" line gives the total number of context switches across all CPUs.
>   
>   The "btime" line gives  the time at which the  system booted, in seconds since
> 

thanks.
-- 
~Randy