On Wed, Nov 20, 2013 at 12:51:21AM -0500, Tejun Heo wrote: >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. Tejun, Yep, hope this will not bring some problem on a large NUMA machie when cpu_distance_fn is not NULL. > >The patch is just extremely marginal. Ah well... why not? I'll apply >it once -rc1 drops. > >Thanks. > >-- >tejun -- Richard Yang Help you, Help me -- 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>