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From: Thomas Gleixner <tglx@linutronix.de>
To: Christoph Lameter <cl@linux.com>
Cc: Richard Cochran <richardcochran@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: Why do we still have 32 bit counters? Interrupt counters overflow within 50 days
Date: Sun, 5 Oct 2014 23:49:14 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1410052331420.4383@nanos> (raw)
In-Reply-To: <alpine.DEB.2.11.1410030706220.8990@gentwo.org>

On Fri, 3 Oct 2014, Christoph Lameter wrote:
> On Fri, 3 Oct 2014, Richard Cochran wrote:
> 
> > >  DECLARE_PER_CPU(char *, irq_stack_ptr);
> > > -DECLARE_PER_CPU(unsigned int, irq_count);
> > > +DECLARE_PER_CPU(unsigned long, irq_count);
> >
> > Still 32 bit on 32 bit machines...
> 
> 64 bit counters on 32 bit machines are not an easy thing and could be

Whats so hard about 64bit counters on 32bit machines?

> expensive to handle in particular because these counters are used in
> performance critical hotpaths.

The expensive overhead is a single "adcl" instruction.

> I thought I better leave it alone on 32 bit.

And how exactly are we supposed to explain the different behaviour to
users?

Thanks,

	tglx

  parent reply	other threads:[~2014-10-05 21:49 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-03  9:45 Why do we still have 32 bit counters? Interrupt counters overflow within 50 days Christoph Lameter
2014-10-03 10:33 ` Thomas Gleixner
2014-10-03 11:54   ` Christoph Lameter
2014-10-03 12:03     ` Richard Cochran
2014-10-03 12:07       ` Christoph Lameter
2014-10-03 12:17         ` Richard Cochran
2014-10-03 14:04           ` Christoph Lameter
2014-10-05 21:49         ` Thomas Gleixner [this message]
2014-10-05 23:24           ` Christoph Lameter
2014-10-05 23:57             ` Eric Dumazet
2014-10-06  8:06             ` Thomas Gleixner
2014-10-06 10:22               ` Christoph Lameter
2014-10-06 13:01                 ` Thomas Gleixner
2014-10-06 15:16                   ` Christoph Lameter
2014-10-06 15:28                     ` Thomas Gleixner
2014-10-06 19:34                       ` Henrique de Moraes Holschuh
2014-10-06 15:31                     ` David Lang
2014-10-06 19:45                       ` Christoph Lameter
2014-10-05 23:59           ` Eric Dumazet
2014-10-06  7:54             ` Thomas Gleixner
2014-10-06 10:49           ` David Lang
2014-10-06 12:28             ` Thomas Gleixner
2014-10-03 12:15     ` Paul Bolle
2014-10-03 12:23       ` Christoph Lameter
2014-10-04 10:26         ` Bernd Petrovitsch

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