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    SubjectRe: [GIT PULL rcu/next] rcu commits for 2.6.40
    On Sat, May 14, 2011 at 10:49:31PM -0700, Yinghai Lu wrote:
    > On 05/14/2011 10:41 PM, Yinghai Lu wrote:
    > > On 05/14/2011 09:14 PM, Yinghai Lu wrote:
    > >> On 05/14/2011 11:34 AM, Paul E. McKenney wrote:
    > >>>> and do the inspection afterwards.
    > >>>
    > >>> And here is a lightly-tested patch, which applies on tip/core/rcu.
    > >>>
    > >>> This problem could account for both the long delays seen with e59fb312
    > >>> (Decrease memory-barrier usage based on semi-formal proof) and the
    > >>> shorter delays seen with a26ac245 (move TREE_RCU from softirq to kthread).
    > >>
    > >> yes. it fixes the problem.
    > >>
    > >> for 1024g system when hotadd mem enabled in kernel config
    > >>
    > >> [ 31.814803] cpu_dev_init done
    > >> [ 35.437163] memory_dev_init done
    > >>
    > >> even it is with gcc from opensuse 11.3
    > >
    > > got:
    > >
    > > [ 86.931217] Switched to NOHz mode on CPU #0
    > > [ 86.931272] Switched to NOHz mode on CPU #25
    > > [ 86.931278] ------------[ cut here ]------------
    > > [ 86.931290] WARNING: at kernel/rcutree.c:364 rcu_enter_nohz+0x44/0x76()
    > > [ 86.931294] Hardware name: Sun Fire X4800 M2
    > > [ 86.931297] Modules linked in:
    > > [ 86.931303] Pid: 0, comm: swapper Not tainted 2.6.39-rc7-tip-yh-04836-g5e42dc2-dirty #3
    > > [ 86.931307] Call Trace:
    > > [ 86.931333] [<ffffffff81080280>] warn_slowpath_common+0x85/0x9d
    > > [ 86.931338] Switched to NOHz mode on CPU #74
    > > [ 86.931346] [<ffffffff810802b2>] warn_slowpath_null+0x1a/0x1c
    > > [ 86.931356] [<ffffffff810d3615>] rcu_enter_nohz+0x44/0x76
    > > [ 86.931370] [<ffffffff810ab3cb>] tick_nohz_stop_sched_tick+0x27d/0x366
    > > [ 86.931381] [<ffffffff810391bc>] cpu_idle+0x7a/0xcc
    > > [ 86.931397] [<ffffffff81bd1aa3>] rest_init+0xb7/0xbe
    > > [ 86.931408] [<ffffffff81bd19ec>] ? csum_partial_copy_generic+0x16c/0x16c
    > > [ 86.931423] [<ffffffff82738e39>] start_kernel+0x3b2/0x3bd
    > > [ 86.931428] Switched to NOHz mode on CPU #94
    > > [ 86.931436] [<ffffffff827382cc>] x86_64_start_reservations+0x9c/0xa0
    > > [ 86.931446] [<ffffffff827384a8>] x86_64_start_kernel+0x1d8/0x1e3
    > > [ 86.931463] ---[ end trace 2cfc591bf7de931f ]---
    > > [ 86.931598] Switched to NOHz mode on CPU #151
    > > [ 86.931613] Switched to NOHz mode on CPU #152
    >
    > it seems gcc from Fedora 14 is not happy with this patch.
    >
    > [ 35.113696] cpu_dev_init done
    > [ 155.963662] memory_dev_init done

    Hmmm... It looks like my attempts to make RCU recover from misnesting are
    not completely foolproof. I will be especially happy to look into this
    if you could look for the source of the irq_enter()/irq_exit() misnesting.

    (And yes, it still might be a bug in my code -- I will be looking at that
    yet again as well.)

    Thanx, Paul


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