Messages in this thread | | | From | Hollis Blanchard <> | Subject | Re: [PATCH] PPC64 iSeries: cleanup viopath | Date | Wed, 16 Mar 2005 09:12:51 -0600 |
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On Mar 15, 2005, at 9:53 AM, Stephen Rothwell wrote:
> On Tue, 15 Mar 2005 08:32:27 -0600 Hollis Blanchard > <hollis@penguinppc.org> 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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