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From: Randy Dunlap <rdunlap@infradead.org>
To: Alexei Lozovsky <me@ilammy.net>, Thomas Gleixner <tglx@linutronix.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>,
	Christoph Lameter <cl@linux.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 7/7] docs: proc.rst: stat: Note the interrupt counter wrap-around
Date: Fri, 10 Sep 2021 20:59:26 -0700	[thread overview]
Message-ID: <a3aa1c2e-fabe-8911-d3ad-555a39ba3234@infradead.org> (raw)
In-Reply-To: <20210911034808.24252-8-me@ilammy.net>

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@ilammy.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


  reply	other threads:[~2021-09-11  4:01 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10  8:53 /proc/stat " Alexei Lozovsky
2021-09-11  3:48 ` [PATCH 0/7] proc/stat: Maintain monotonicity of "intr" and "softirq" Alexei Lozovsky
2021-09-11  3:48   ` [PATCH 1/7] genirq: Use unsigned int for irqs_sum Alexei Lozovsky
2021-09-11  3:48   ` [PATCH 2/7] powerpc/irq: arch_irq_stat_cpu() returns unsigned int Alexei Lozovsky
2021-09-11  3:48   ` [PATCH 3/7] x86/irq: " Alexei Lozovsky
2021-09-11  3:48   ` [PATCH 4/7] x86/irq: arch_irq_stat() " Alexei Lozovsky
2021-09-11  3:48   ` [PATCH 5/7] proc/stat: Use unsigned int for "intr" sum Alexei Lozovsky
2021-09-11  3:48   ` [PATCH 6/7] proc/stat: Use unsigned int for "softirq" sum Alexei Lozovsky
2021-09-11  3:48   ` [PATCH 7/7] docs: proc.rst: stat: Note the interrupt counter wrap-around Alexei Lozovsky
2021-09-11  3:59     ` Randy Dunlap [this message]
2021-09-12  9:30   ` [PATCH 0/7] proc/stat: Maintain monotonicity of "intr" and "softirq" Alexey Dobriyan
2021-09-12 12:37     ` Alexei Lozovsky
2021-09-14 14:11       ` Thomas Gleixner
2021-09-15  4:24         ` Alexei Lozovsky
2021-09-15 17:58   ` [PATCH v2 00/12] " Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 01/12] genirq: Use READ_ONCE for IRQ counter reads Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 02/12] genirq: Use unsigned long for IRQ counters Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 03/12] powerpc/irq: Use READ_ONCE for IRQ counter reads Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 04/12] powerpc/irq: Use unsigned long for IRQ counters Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 05/12] powerpc/irq: Use unsigned long for IRQ counter sum Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 06/12] x86/irq: Use READ_ONCE for IRQ counter reads Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 07/12] x86/irq: Use unsigned long for IRQ counters Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 08/12] x86/irq: Use unsigned long for IRQ counters more Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 09/12] x86/irq: Use unsigned long for IRQ counter sum Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 10/12] proc/stat: Use unsigned long for "intr" sum Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 11/12] proc/stat: Use unsigned long for "softirq" sum Alexei Lozovsky
2021-09-15 17:58     ` [PATCH v2 12/12] docs: proc.rst: stat: Note the interrupt counter wrap-around Alexei Lozovsky

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