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From: Tejun Heo <tj@kernel.org>
To: Christoph Lameter <cl@linux.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	Pekka Enbeerg <penberg@cs.helsinki.fi>,
	linux-kernel@vger.kernel.org,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	akpm@linux-foundation.org
Subject: Re: x86: A fast way to check capabilities of the current cpu
Date: Fri, 21 Jan 2011 18:11:33 +0100	[thread overview]
Message-ID: <20110121171133.GI2832@htj.dyndns.org> (raw)
In-Reply-To: <alpine.DEB.2.00.1012151404070.21102@router.home>

Hello, Christoph.

I was trying to forward this to x86 tree but spotted a problem.

On Wed, Dec 15, 2010 at 02:07:39PM -0600, Christoph Lameter wrote:
> +static __always_inline int this_cpu_constant_test_bit(unsigned int nr,
> +                        const unsigned long __percpu *addr)
> +{
> +	unsigned long __percpu *a = (unsigned long *)addr + nr / BITS_PER_LONG;
> +
> +	return ((1UL << (nr % BITS_PER_LONG)) & percpu_read_stable(*a)) != 0;
> +}

I don't think percpu_read_stable() can be used here.  It's not
guaranteed to be stable across different cpus.

Also, can we just implement what's necessary on top of this_cpu_has()?
this_cpu_has() already has constant handling, so there's no need to
add this_cpu_test_bit() at this point.

Thank you.

-- 
tejun

  parent reply	other threads:[~2011-01-21 17:11 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-12-15 20:07 Christoph Lameter
2010-12-15 20:11 ` x86: Avoid passing struct cpuinfo pointer to mce_available Christoph Lameter
2010-12-15 20:56 ` x86: A fast way to check capabilities of the current cpu Andrew Morton
2010-12-15 21:03   ` H. Peter Anvin
2010-12-15 21:30     ` Miguel Ojeda
2010-12-15 21:39       ` H. Peter Anvin
2010-12-15 21:48         ` Miguel Ojeda
2010-12-16  6:25         ` Miles Bader
2010-12-16 10:17           ` Miguel Ojeda
2010-12-16 10:29             ` Miles Bader
2010-12-16 15:38               ` H. Peter Anvin
2010-12-17  4:26                 ` Miles Bader
2011-01-21 17:11 ` Tejun Heo [this message]
2011-01-21 17:21   ` Christoph Lameter
2011-01-21 17:28     ` Tejun Heo
2011-01-21 17:46       ` Christoph Lameter
2011-01-21 17:48         ` Tejun Heo
2011-01-21 17:57           ` Christoph Lameter
2011-01-21 18:12             ` Tejun Heo
2011-01-21 18:20               ` Christoph Lameter
2011-01-21 22:32         ` H. Peter Anvin
2011-01-24 17:05           ` Christoph Lameter

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