[openib-general] Re: [PATCH 18 of 20] ipath - kbuild infrastructure

[Bryan O'Sullivan]

On Mon, 2006-03-13 at 19:10 +0100, Adrian Bunk wrote:

> I'm still a bit surprised, since in the rest of the kernel we are even 
> going from -O2 to -Os for getting better performance.
> 
> Robert said he wanted to post some numbers showing that -O3 is 
> measurably better for you [1], but I haven't seen them.

I just ran some numbers.  At large packet sizes, it doesn't matter what
options we use, because we spend all of our time in __iowrite_copy32,
which uses the string copy instructions.

For small packets, my quick tests indicate that -Os gives about 5%
*better* performance than -O3 (using gcc 4 on FC4).  This is in line
with what people have been finding in the kernel in general recently.

So if I change that CFLAGS line from -O3 to -Os, are we in OK
shape?  :-)

> > +_ipath_idstr:="PathScale $(shell date +%F)"
> > +EXTRA_CFLAGS += -DIPATH_IDSTR='$(_ipath_idstr)' -DIPATH_KERN_TYPE=0
> >...
> 
> UTS_VERSION is already available and printed at the top of dmesg.
> I don't see the point in printing it a second time.

Good point.  The idstr stuff is for our out-of-tree drivers.

Thanks,

	<b