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From: Fortini Matteo <matteo.fortini@mta.it>
To: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Recommended functions for accessing internal registers
Date: Tue, 1 Dec 2009 17:44:21 +0100	[thread overview]
Message-ID: <4B1547E5.6050301@mta.it> (raw)

I see that throughout the kernel source, internal PPC registers are 
accessed through [in|out]_be[32|16|8]() functions. However, they are 
translated into 3 inline assembly instructions, one of which is an 
isync, which has a huge performance hit.
I tried using readl_be() which seems to be the right function according 
to the Documentation/ dir, but it is translated directly to in_be32(), 
so no luck.

Is it really necessary to use all those instructions? I know I could use 
a (volatile u32 *) variable to avoid subsequent read/writes to be 
optimized out, but it seems to be a deprecated use.

Thank you in advance,
Matteo

             reply	other threads:[~2009-12-01 17:22 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-12-01 16:44 Fortini Matteo [this message]
2009-12-02 20:57 ` Recommended functions for accessing internal registers Benjamin Herrenschmidt
2009-12-03 11:16   ` Fortini Matteo
2009-12-03 21:10     ` Benjamin Herrenschmidt

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