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Message-ID: <20110524011824.GL7428@linux.vnet.ibm.com> Date: Mon, 23 May 2011 18:18:24 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Yinghai Lu <yinghai@...nel.org> Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com, tglx@...utronix.de, mingo@...e.hu Subject: Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof" On Mon, May 23, 2011 at 03:58:45PM -0700, Yinghai Lu wrote: > On 05/23/2011 03:55 PM, Yinghai Lu wrote: > > On 05/23/2011 03:01 PM, Yinghai Lu wrote: > >> On 05/23/2011 02:25 PM, Paul E. McKenney wrote: > >>> On Mon, May 23, 2011 at 01:14:22PM -0700, Yinghai Lu wrote: > >>>> On 05/21/2011 07:08 AM, Paul E. McKenney wrote: > >>>>> On Sat, May 21, 2011 at 06:18:44AM -0700, Paul E. McKenney wrote: > >>>>>> On Fri, May 20, 2011 at 05:02:40PM -0700, Yinghai Lu wrote: > >>>>>>> On 05/20/2011 04:49 PM, Paul E. McKenney wrote: > >>>>>>>> On Fri, May 20, 2011 at 04:16:28PM -0700, Yinghai Lu wrote: > >>>>>>> ... > >>>>>>>>> > >>>>>>>>> the same one i sent out before, but let DEBUG_LOCKING_API_SELFTESTS disabled. > >>>>>>>> > >>>>>>>> OK, just to make sure I understand... You are compiling exactly the > >>>>>>>> same kernel source tree with exactly the same .config, just with two > >>>>>>>> different versions of gcc, correct? > >>>>>>> yes. > >>>>>>>> > >>>>>>>> If so, it is quite possible that the slow one is the correct one. :-/ > >>>>>>> yeah, new version always have problem. > >>>>>>> > >>>>>>> looks like opensuse11.3 has 4.5.0 and fedora14 has 4.5.1 > >>>>>> > >>>>>> OK, so fedora14 is the fast one (4.5.1) and opensuse11.3 is the slow > >>>>>> one (4.5.0), correct? > >>>>> > >>>>> And does commit c7a3786030 help? This commit (from Peter Zijlstra) > >>>>> tidied up RCU kthreads' scheduler interactions. The patch is below, > >>>>> though it is probably more convenient to pull it from the rcu/next > >>>>> branch of: > >>>>> > >>>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git > >>>>> > >>> > > gcc in Fedora 14 is fine with your tree. > > > > sorry, I should wait for longer to see Fedora 14 is ok. > > got same warning with the one compiled from fedora 14... > > [ 372.937251] INFO: task rcun0:8 blocked for more than 120 seconds. > [ 372.937618] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 372.956130] rcun0 D 0000000000000000 0 8 2 0x00000000 > [ 372.956498] ffff882070d65e90 0000000000000046 ffff882070d64000 0000000000004000 > [ 372.956528] 00000000001d1f40 ffff882070d65fd8 00000000001d1f40 ffff882070d65fd8 > [ 372.956555] 0000000000004000 00000000001d1f40 ffff882070d18000 ffff882070d6a2b0 > [ 372.956581] Call Trace: > [ 372.956605] [<ffffffff810afce3>] ? __lock_release+0x166/0x16f > [ 372.956624] [<ffffffff81c229d1>] ? _raw_spin_unlock_irqrestore+0x3f/0x46 > [ 372.956639] [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137 > [ 372.956650] [<ffffffff810adfd5>] ? trace_hardirqs_on+0xd/0xf > [ 372.956661] [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137 > [ 372.956673] [<ffffffff8109a0a5>] kthread+0x8c/0xa8 > [ 372.956689] [<ffffffff81c2a754>] kernel_thread_helper+0x4/0x10 > [ 372.956701] [<ffffffff81c22c80>] ? retint_restore_args+0xe/0xe > [ 372.956711] [<ffffffff8109a019>] ? __init_kthread_worker+0x5b/0x5b > [ 372.956722] [<ffffffff81c2a750>] ? gs_change+0xb/0xb > [ 372.956726] INFO: lockdep is turned off. > [ 492.750827] INFO: task rcun0:8 blocked for more than 120 seconds. > [ 492.751150] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 492.762991] rcun0 D 0000000000000000 0 8 2 0x00000000 > [ 492.763264] ffff882070d65e90 0000000000000046 ffff882070d64000 0000000000004000 > [ 492.763294] 00000000001d1f40 ffff882070d65fd8 00000000001d1f40 ffff882070d65fd8 > [ 492.763320] 0000000000004000 00000000001d1f40 ffff882070d18000 ffff882070d6a2b0 > [ 492.763346] Call Trace: > [ 492.763359] [<ffffffff810afce3>] ? __lock_release+0x166/0x16f > [ 492.763371] [<ffffffff81c229d1>] ? _raw_spin_unlock_irqrestore+0x3f/0x46 > [ 492.763382] [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137 > [ 492.763393] [<ffffffff810adfd5>] ? trace_hardirqs_on+0xd/0xf > [ 492.763404] [<ffffffff810ce941>] ? rcu_cpu_kthread_should_stop+0x137/0x137 > [ 492.763414] [<ffffffff8109a0a5>] kthread+0x8c/0xa8 > [ 492.763427] [<ffffffff81c2a754>] kernel_thread_helper+0x4/0x10 > [ 492.763439] [<ffffffff81c22c80>] ? retint_restore_args+0xe/0xe > [ 492.763449] [<ffffffff8109a019>] ? __init_kthread_worker+0x5b/0x5b > [ 492.763460] [<ffffffff81c2a750>] ? gs_change+0xb/0xb > [ 492.763463] INFO: lockdep is turned off. > > if reverting PeterZ's patch will not have that warning. OK, so it looks like I need to get this out of the way in order to track down the delays. Or does reverting PeterZ's patch get you a stable system, but with the longish delays in memory_dev_init()? If the latter, it might be more productive to handle the two problems separately. For whatever it is worth, I do see about 5% increase in grace-period duration when switching to kthreads. This is acceptable -- your 30x increase clearly is completely unacceptable and must be fixed. Other than that, the main thing that affects grace period duration is the setting of CONFIG_HZ -- the smaller the HZ value, the longer the grace-period duration. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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