svn commit: r221855 - in head/sys: amd64/include arm/include dev/md dev/null i386/include ia64/include mips/include powerpc/include sparc64/include sun4v/include sys vm

[Marius Strobl]

On Fri, May 13, 2011 at 03:41:10PM -0500, Alan Cox wrote:
> On 5/13/2011 2:35 PM, Matthew D Fleming wrote:
> >Author: mdf
> >Date: Fri May 13 19:35:01 2011
> >New Revision: 221855
> >URL: http://svn.freebsd.org/changeset/base/221855
> >
> >Log:
> >   Move the ZERO_REGION_SIZE to a machine-dependent file, as on many
> >   architectures (i386, for example) the virtual memory space may be
> >   constrained enough that 2MB is a large chunk.  Use 64K for arches
> >   other than amd64 and ia64, with special handling for sparc64 due to
> >   differing hardware.
> >
> >   Also commit the comment changes to kmem_init_zero_region() that I
> >   missed due to not saving the file.  (Darn the unfamiliar development
> >   environment).
> >
> >   Arch maintainers, please feel free to adjust ZERO_REGION_SIZE as you
> >   see fit.
> >
> >   Requested by:	alc
> >   MFC after:	1 week
> >   MFC with:	r221853
> 
> I would encourage people on platforms with virtually indexed data caches 
> to do a simple before and after performance test on this change, like 
> "dd if=/dev/zero of=/dev/null bs=64k", just to make sure that there are 
> no performance regressions.
> 

Actually, this improved the performance on an old 500MHz USIIe quite
a bit, with r221854:
v100# dd if=/dev/zero of=/dev/null bs=64k count=100000
100000+0 records in
100000+0 records out
6553600000 bytes transferred in 13.523223 secs (484618204 bytes/sec)

with r221855:
v100# dd if=/dev/zero of=/dev/null bs=64k count=100000
100000+0 records in
100000+0 records out
6553600000 bytes transferred in 5.235192 secs (1251835639 bytes/sec)

Repeated runs vary only marginally in both cases.

Marius