linux-kernel - Re: x86: A fast way to check capabilities of the current cpu

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Message-ID: <4D093580.9000303@zytor.com>
Date:	Wed, 15 Dec 2010 13:39:12 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>, Tejun Heo <tj@...nel.org>,
	Pekka Enbeerg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: x86: A fast way to check capabilities of the current cpu

On 12/15/2010 01:30 PM, Miguel Ojeda wrote:
> 
> In this case it this_cpu_*_test_bit() return an int, but they act as a
> bool and are used in if()s; where is the catch?
> 

If they aren't, and are stored in a variable for whatever reason, then
the || form will generate additional instructions to booleanize the
value for no good reason.

	-hpa
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