On 04/02/16 12:04, Juri Lelli wrote: > On 04/02/16 09:54, Juri Lelli wrote: > > Hi Steve, > > > > first of all thanks a lot for your detailed report, if only all bug > > reports were like this.. :) > > > > On 03/02/16 13:55, Steven Rostedt wrote: > > [...] > > > > > Right. I think this is the same thing that happens after hotplug. IIRC > > the code paths are actually the same. The problem is that hotplug or > > cpuset reconfiguration operations are destructive w.r.t. root_domains, > > so we lose bandwidth information when that happens. The problem is that > > we only store cumulative information regarding bandwidth in root_domain, > > while information about which task belongs to which cpuset is store in > > cpuset data structures. > > > > I tried to fix this a while back, but my tentative was broken, I failed > > to get locking right and, even though it seemed to fix the issue for me, > > it was prone to race conditions. You might still want to have a look at > > that for reference: https://lkml.org/lkml/2015/9/2/162 > > > > [...] > > > > > It's good that we can recover, but that's still a bug yes :/. > > > > I'll try to see if my broken patch make what you are seeing apparently > > disappear, so that we can at least confirm that we are seeing the same > > problem; you could do the same if you want, I pushed that here > > > > No it doesn't solve this :/. I placed restoring code in the hotplug > workfn, so updates generated by toggling sched_load_balance don't get > caught, of course. But, this at least tells us that we should solve this > someplace else. >
Well, if I call an unlocked version of my cpuset_hotplug_update_rd() from kernel/cpuset.c:update_flag() the issue seems to go away. But, we end up overcommitting the default null domain (try to toggle sched_load_ balance multiple times). I updated the branch, but I still think we should solve this differently. Best, - Juri