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From: Alexei Lozovsky <me@ilammy.net>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Christoph Lameter <cl@linux.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 0/7] proc/stat: Maintain monotonicity of "intr" and "softirq"
Date: Sun, 12 Sep 2021 21:37:20 +0900	[thread overview]
Message-ID: <44F84890-521F-4BCA-9F48-B49D2C8A9E32@ilammy.net> (raw)
In-Reply-To: <YT3In8SWc2eYZ/09@localhost.localdomain>

On Sun, Sep 12, 2021, at 18:30, Alexey Dobriyan wrote:
> How about making everything "unsigned long" or even "u64" like NIC
> drivers do?

I see some possible hurdles ahead:

- Not all architectures have atomic operations for 64-bit values

  All those "unsigned int" counters are incremented with __this_cpu_inc()
  which tries to use atomics if possible. Though, I'm not quite sure
  how this works for read side which does not seem to use atomic reads
  at all. I guess, just by the virtue of properly aligned 32-bit reads
  being atomic everywhere? If that's so, I think widening counters to
  64 bits will come with an asterisk.

- We'll need to update all counters to be 64-bit.

  Like, *everyone*. Every field that gets summed up needs to be 64-bit
  (or else wrap-arounds will be incorrect). Basically every counter in
  every irq_cpustat_t will need to become twice as wide. If that's
  a fine price to pay for accurate, full-width counters...

  Previously I thought that some of these counters even come from
  hardware, but now that I'm reviewing them, that does not seem to be
  the case. Thankfully.

So right now I don't see why it shouldn't be doable in theory.
I'll give it a shot, I guess, and see how it works in practice,
at least as far as the patches go (since I can't really test on all
architectures).

  reply	other threads:[~2021-09-12 12:37 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10  8:53 /proc/stat interrupt counter wrap-around 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
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 [this message]
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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