On Tue, 2012-10-09 at 08:56 -0600, Mike Yoknis wrote: > On Mon, 2012-10-08 at 16:16 +0100, Mel Gorman wrote: > > On Wed, Oct 03, 2012 at 08:56:14AM -0600, Mike Yoknis wrote: > > > memmap_init_zone() loops through every Page Frame Number (pfn), > > > including pfn values that are within the gaps between existing > > > memory sections. The unneeded looping will become a boot > > > performance issue when machines configure larger memory ranges > > > that will contain larger and more numerous gaps. > > > > > > The code will skip across invalid sections to reduce the > > > number of loops executed. > > > > > > Signed-off-by: Mike Yoknis <mike.yoknis@xxxxxx> > > > > I do not see the need for > > the additional complexity unless you can show it makes a big difference > > to boot times. > > > > Mel, > > Let me pass along the numbers I have. We have what we call an > "architectural simulator". It is a computer program that pretends that > it is a computer system. We use it to test the firmware before real > hardware is available. We have booted Linux on our simulator. As you > would expect it takes longer to boot on the simulator than it does on > real hardware. > > With my patch - boot time 41 minutes > Without patch - boot time 94 minutes > > These numbers do not scale linearly to real hardware. But indicate to > me a place where Linux can be improved. > > Mike Yoknis > Mel, I finally got access to prototype hardware. It is a relatively small machine with only 64GB of RAM. I put in a time measurement by reading the TSC register. I booted both with and without my patch - Without patch - [ 0.000000] Normal zone: 13400064 pages, LIFO batch:31 [ 0.000000] memmap_init_zone() enter 1404184834218 [ 0.000000] memmap_init_zone() exit 1411174884438 diff = 6990050220 With patch - [ 0.000000] Normal zone: 13400064 pages, LIFO batch:31 [ 0.000000] memmap_init_zone() enter 1555530050778 [ 0.000000] memmap_init_zone() exit 1559379204643 diff = 3849153865 This shows that without the patch the routine spends 45% of its time spinning unnecessarily. Mike Yoknis -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
