Re: [GIT PULL rcu/next] rcu commits for 2.6.40

[Paul E. McKenney]

On Sat, May 14, 2011 at 11:04:15PM -0700, Paul E. McKenney wrote:
> 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.)

And the way you can prove that it is my code rather than the arch
code is to show that the warning happens on your system when the
irq_enter()/irq_exit() calls are perfectly nested.

							Thanx, Paul
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