Am 16.09.2015 um 14:22 schrieb Oleg Nesterov: >> The issue is that rcu_sync doesn't eliminate synchronize_sched, > > Yes, but it eliminates _expedited(). This is good, but otoh this means > that (say) individual __cgroup_procs_write() can take much more time. > However, it won't block the readers and/or disturb the whole system. > And percpu_up_write() doesn't do synchronize_sched() at all. > >> it only >> makes it more rare. > > Yes, so we can hope that multiple __cgroup_procs_write()'s can "share" > a single synchronize_sched(). And in fact it does. Paolo suggested to trace how often we call synchronize_sched so I applied some advanced printk debugging technology ;-) Until login I have 41 and after starting the 70 guests this went up to 48. Nice work. > >> So it's possible that it isn't eliminating the root >> cause of the problem. > > We will see... Just in case, currently the usage of percpu_down_write() > is suboptimal. We do not need to do ->sync() under cgroup_mutex. But > this needs some WIP changes in rcu_sync. Plus we can do more improvements, > but this is off-topic right now. > > Oleg. > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
