Hello, On Wed, Nov 20, 2013 at 11:00:56AM +0800, Wei Yang wrote: > What do you think about this one? > > > > >From bd70498b9df47b25ff20054e24bb510c5430c0c3 Mon Sep 17 00:00:00 2001 > >From: Wei Yang <weiyang@xxxxxxxxxxxxxxxxxx> > >Date: Thu, 10 Oct 2013 09:42:14 +0800 > >Subject: [PATCH] percpu: optimize group assignment when cpu_distance_fn is > > NULL > > > >When cpu_distance_fn is NULL, all CPUs belongs to group 0. The original logic > >will continue to go through each CPU and its predecessor. cpu_distance_fn is > >always NULL when pcpu_build_alloc_info() is called from pcpu_page_first_chunk(). > > > >By applying this patch, the time complexity will drop to O(n) form O(n^2) in > >case cpu_distance_fn is NULL. The test was put in the inner loop because the nesting was already too deep and cpu_distance_fn is unlikely to be NULL on machines where the number of CPUs is high enough to matter. If that O(n^2) loop is gonna be a problem, it's gonna be a problem on large NUMA machines and we'll have to do something about it for cases where cpu_distance_fn exists anyway. The patch is just extremely marginal. Ah well... why not? I'll apply it once -rc1 drops. Thanks. -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>