On Mar 15, 2005, at 9:53 AM, Stephen Rothwell wrote:
On Tue, 15 Mar 2005 08:32:27 -0600 Hollis Blanchard <[EMAIL PROTECTED]> wrote:
On Mar 14, 2005, at 9:34 PM, Stephen Rothwell wrote:
Since you brought this file to my attention, I figured I might as well
do
some simple cleanups. This patch does:
- single bit int bitfields are a bit suspect and Anndrew pointed
out recently that they are probably slower to access than ints
--- linus/arch/ppc64/kernel/viopath.c 2005-03-13 04:07:42.000000000 +1100 +++ linus-cleanup.1/arch/ppc64/kernel/viopath.c 2005-03-15 14:02:48.000000000 +1100 @@ -56,8 +57,8 @@ * But this allows for other support in the future. */ static struct viopathStatus { - int isOpen:1; /* Did we open the path? */ - int isActive:1; /* Do we have a mon msg outstanding */ + int isOpen; /* Did we open the path? */ + int isActive; /* Do we have a mon msg outstanding */ int users[VIO_MAX_SUBTYPES]; HvLpInstanceId mSourceInst; HvLpInstanceId mTargetInst;
Why not use a byte instead of a full int (reordering the members for alignment)?
Because "classical" boleans are ints.
Because I don't know the relative speed of accessing single byte variables.
I didn't see the original observation that bitfields are slow. If the argument was that loading a bitfield requires a load then mask, then you'll be happy to find that PPC has word, halfword, and byte load instructions. So loading a byte (unsigned, as Brad pointed out) should be just as fast as loading a word.
It really makes little difference, I was just trying to get rid of the silly signed single bit bitfields ...
I understand. I was half being nitpicky, and half wondering if there was an actual reason I was missing.
-Hollis
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