linux-kernel - Why do we still have 32 bit counters? Interrupt counters overflow within 50 days

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Message-ID: <alpine.DEB.2.11.1410030435260.8324@gentwo.org>
Date:	Fri, 3 Oct 2014 04:45:08 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	linux-kernel@...r.kernel.org
Subject: Why do we still have 32 bit counters? Interrupt counters overflow
 within 50 days

struct irq_desc still has

  unsigned int irq_count;

A timer interrupt occurs 1000 times per second and there are 86400 seconds
in a day. There is a counter for the local timer interrupt that needs to
be continually incremented.

So the counter will overflow in

2^32 / 1000 / 86400 = 46 days

Diagnostic tools will be surprised by the counters suddenly going back to
zero. There may be other interrupt sources that also occur quite often.

Is this the way its intended or should the counters be expanded to 64 bit?

64 bit would last for our lifetime.

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