* Qiang Huang | 2013-04-25 17:01:18 [+0800]: >This is revert of "sched-clear-pf-thread-bound-on-fallback-rq.patch" >(commit 0d939066acdcb in v3.4-rt),. > >Select_fallback_rq() can be easilly called during system boot, because >select_task_rq_fair() just return task_cpu(p) for bounded kernel threads, >which is 0 during system boot and not in tsk_cpus_allowed, so >select_fallback_rq() is called and PF_THREAD_BOUND is cleared. In my >box, 1/3 bounded kernel threads will clear that flag after boot. > >And it will cause problems, for example: ># for pid in `ps -e -o pid`; do taskset -p -c 0-15 $pid; done >this command will cause system hung. > >What's more, I don't see why we need to clear this flag any more, >because "cpu/rt: Rework cpu down for PREEMPT_RT" already remove the >optimization for PF_THREAD_BOUND on migrate_disable/enable. > >Signed-off-by: Qiang Huang <h.huangqiang@xxxxxxxxxx> I can execute the command you mendtion above on v3.4 and v3.8 with no hangs. Can you give me number of your cpus and maybe the config or another detail? I played a little with it on v3.8. That code you asked to remove triggers only on cpu down for kernel threads which do not use the park/unpark infrastructure that is "posixcputmr" and "migration" which get removed later. The only reason why "migration" pops up is so it can leave. I managed to trigger it as well for worker threads. The threads which were bound the CPU, that went down, are marked DISASSOCIATED in gcwq_unbind_fn() and we lose that PF_THREAD_BOUND flag once that thread is used. After the CPU gets back, it is assigned to the "old" cpu via worker_maybe_bind_and_lock() and the PF_THREAD_BOUND flag is missing. So that is not looking that good. Will look at this later. Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
