On Tue, Apr 26, 2011 at 09:17:28PM +0200, Sedat Dilek wrote: > On Tue, Apr 26, 2011 at 8:50 PM, Paul E. McKenney > <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > On Tue, Apr 26, 2011 at 10:12:39AM -0700, Linus Torvalds wrote: > >> On Tue, Apr 26, 2011 at 9:38 AM, Bruno Prémont > >> <bonbons@xxxxxxxxxxxxxxxxx> wrote: > >> > > >> > Here it comes: > >> > > >> > rcu_kthread (when build processes are STOPped): > >> > [ 836.050003] rcu_kthread R running 7324 6 2 0x00000000 > >> > [ 836.050003] dd473f28 00000046 5a000240 dd65207c dd407360 dd651d40 0000035c dd473ed8 > >> > [ 836.050003] c10bf8a2 c14d63d8 dd65207c dd473f28 dd445040 dd445040 dd473eec c10be848 > >> > [ 836.050003] dd651d40 dd407360 ddfdca00 dd473f14 c10bfde2 00000000 00000001 000007b6 > >> > [ 836.050003] Call Trace: > >> > [ 836.050003] [<c10bf8a2>] ? check_object+0x92/0x210 > >> > [ 836.050003] [<c10be848>] ? init_object+0x38/0x70 > >> > [ 836.050003] [<c10bfde2>] ? free_debug_processing+0x112/0x1f0 > >> > [ 836.050003] [<c103d9fd>] ? lock_timer_base+0x2d/0x70 > >> > [ 836.050003] [<c13c8ec7>] schedule_timeout+0x137/0x280 > >> > >> Hmm. > >> > >> I'm adding Ingo and Peter to the cc, because this whole "rcu_kthread > >> is running, but never actually running" is starting to smell like a > >> scheduler issue. > >> > >> Peter/Ingo: RCUTINY seems to be broken for Bruno. During any kind of > >> heavy workload, at some point it looks like rcu_kthread simply stops > >> making any progress. It's constantly in runnable state, but it doesn't > >> actually use any CPU time, and it's not processing the RCU callbacks, > >> so the RCU memory freeing isn't happening, and slabs just build up > >> until the machine dies. > >> > >> And it really is RCUTINY, because the thing doesn't happen with the > >> regular tree-RCU. > > > > The difference between TINY_RCU and TREE_RCU is that TREE_RCU still uses > > softirq for the core RCU processing. TINY_RCU switched to a kthread > > when I implemented RCU priority boosting. There is a similar change in > > my -rcu tree that makes TREE_RCU use kthreads, and Sedat has been running > > into a very similar problem with that change in place. Which is why I > > do not yet push it to the -next tree. > > > >> This is without CONFIG_RCU_BOOST_PRIO, so we basically have > >> > >> struct sched_param sp; > >> > >> rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread"); > >> sp.sched_priority = RCU_BOOST_PRIO; > >> sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp); > >> > >> where RCU_BOOST_PRIO is 1 for the non-boost case. > > > > Good point! Bruno, Sedat, could you please set CONFIG_RCU_BOOST_PRIO to > > (say) 50, and see if this still happens? (I bet that you do, but...) > > > > What's with CONFIG_RCU_BOOST_DELAY setting? CONFIG_RCU_BOOST_DELAY controls how long preemptible RCU lets a grace period run before boosting the priority of any blocked RCU readers. It is completely irrelevant if the rcu_kthread task isn't getting a chance to run, though. This is because it is the rcu_kthread task that does the boosting. > Are those values OK? > > $ egrep 'M486|M686|X86_UP|CONFIG_SMP|NR_CPUS|PREEMPT|_RCU|_HIGHMEM|PAE' .config > CONFIG_TREE_PREEMPT_RCU=y > CONFIG_PREEMPT_RCU=y > CONFIG_RCU_TRACE=y > CONFIG_RCU_FANOUT=32 > # CONFIG_RCU_FANOUT_EXACT is not set > CONFIG_TREE_RCU_TRACE=y > CONFIG_RCU_BOOST=y I suggest CONFIG_RCU_BOOST=n to keep things simple for the moment, but CONFIG_RCU_BOOST=y should be OK too. > CONFIG_RCU_BOOST_PRIO=50 > CONFIG_RCU_BOOST_DELAY=500 > CONFIG_SMP=y > # CONFIG_M486 is not set > CONFIG_M686=y I don't have an opinion on CONFIG_M486 vs. CONFIG_M686. > CONFIG_NR_CPUS=32 > # CONFIG_PREEMPT_NONE is not set > # CONFIG_PREEMPT_VOLUNTARY is not set > CONFIG_PREEMPT=y > CONFIG_HIGHMEM4G=y > # CONFIG_HIGHMEM64G is not set > CONFIG_HIGHMEM=y > CONFIG_DEBUG_OBJECTS_RCU_HEAD=y > CONFIG_DEBUG_PREEMPT=y The above two could be left out, but shouldn't hurt. > # CONFIG_SPARSE_RCU_POINTER is not set > # CONFIG_DEBUG_HIGHMEM is not set > CONFIG_RCU_TORTURE_TEST=m > CONFIG_RCU_CPU_STALL_TIMEOUT=60 > CONFIG_RCU_CPU_STALL_VERBOSE=y > CONFIG_PREEMPT_TRACER=y So they look fine to me, the ones that I understand, anyway. ;-) Thanx, Paul > > - Sedat - > > >> Is that so low that even the idle thread will take priority? It's a UP > >> config with PREEMPT_VOLUNTARY. So pretty much _all_ the stars are > >> aligned for odd scheduling behavior. > >> > >> Other users of SCHED_FIFO tend to set the priority really high (eg > >> "MAX_RT_PRIO-1" is clearly the default one - softirq's, watchdog), but > >> "1" is not unheard of either (touchscreen/ucb1400_ts and > >> mmc/core/sdio_irq), and there are some other random choises out tere. > >> > >> Any ideas? > > > > I have found one bug so far in my code, but it only affects TREE_RCU > > in my -rcu tree, and even then only if HOTPLUG_CPU is enabled. I am > > testing a fix, but I expect Sedat's tests to still break. > > > > I gave Sedat a patch that make rcu_kthread() run at normal (non-realtime) > > priority, and he did not see the failure. So running non-realtime at > > least greatly reduces the probability of failure. > > > > Thanx, Paul > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>