On 03/23/2015 02:41 PM, Peter Zijlstra wrote:
On Tue, Mar 03, 2015 at 09:38:11AM +0100, Vincent Guittot wrote:
Prefer siblings logic dates back to https://lkml.org/lkml/2009/8/27/210 and only used in update_sd_lb_stats() where we have
if (child && child->flags & SD_PREFER_SIBLING) prefer_sibling = 1;
However what confuses me is why should we even look at a child domain's flag to balance tasks across the current sched domain? Why cant we just set and use a sd flag at current level than to look at child domain flag?
Peter, have you got some insight about the reason ?
Yeah, because it makes sense that way? ;-)
The we want to move things to the child's sibling, not the parent's sibling. We further need to have a child for this to make sense.
+1. The above is precisely why we need this patch.
Regards Preeti U Murthy