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Date: Sat, 13 Dec 2014 10:53:35 -0500
From: Sasha Levin <sasha.levin@oracle.com>
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To: Ingo Molnar <mingo@kernel.org>
CC: paulmck@linux.vnet.ibm.com, David Lang <david@lang.hm>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Jones <davej@redhat.com>, Chris Mason <clm@fb.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        =?windows-1252?Q?D=E2niel_Fraga?= <fragabr@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: frequent lockups in 3.18rc4
References: <CA+55aFxVeti8pU=Y_w54oGb8syGduOySAp-ag+KsCom-c12e-Q@mail.gmail.com> <1417806247.4845.1@mail.thefacebook.com> <CA+55aFz3iUyV9=_rVUdO0WPoOyOKOYkcHCxb3p=2fgSHtCTNgw@mail.gmail.com> <20141211145408.GB16800@redhat.com> <CA+55aFy1_w1NrkeopMXsxGftO5F03JzKgn-8uTQRnEAXuoiXgg@mail.gmail.com> <20141212185454.GB4716@redhat.com> <CA+55aFw7vJkuJ9RtVS3yhPsqDos+ii1kdJBZEeoxhb9c2=rStQ@mail.gmail.com> <alpine.DEB.2.02.1412121157060.18579@nftneq.ynat.uz> <20141212203417.GE25340@linux.vnet.ibm.com> <548B5CEC.1040607@oracle.com> <20141213083055.GI32572@gmail.com>
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On 12/13/2014 03:30 AM, Ingo Molnar wrote:
>> > This is my no_hz related config:
>> > 
>> > $ grep NO_HZ .config
>> > CONFIG_NO_HZ_COMMON=y
>> > # CONFIG_NO_HZ_IDLE is not set
>> > CONFIG_NO_HZ_FULL=y
>> > CONFIG_NO_HZ_FULL_ALL=y
> Just curious, if you disable NO_HZ_FULL_ALL, does the bug change?

On 12/13/2014 07:08 AM, Paul E. McKenney wrote:
> Alternatively, your could boot with nohz_full=2-27 (or maybe even
> nohz_full=4-27).  This will override CONFIG_NO_HZ_FULL_ALL=y and will
> provide two (or four with 4-27) housekeeping CPUs that are available to
> run things like RCU grace-period kthreads and RCU callback processing.
> This might allow RCU to get the CPU bandwidth it needs despite
> competition from your workload.

I've tried both nohz_full=4-27 and disabling CONFIG_NO_HZ_FULL_ALL
altogether, but I'm still seeing the stall:

[  725.670017] INFO: rcu_preempt detected stalls on CPUs/tasks:
[  725.670017]  0: (11 ticks this GP) idle=bbd/140000000000002/0 softirq=11529/11529 fqs=0 last_accelerate: 9d0e/a648, nonlazy_posted: 721357, ..
[  725.670017]  (detected by 16, t=2102 jiffies, g=9857, c=9856, q=2581)
[  725.670017] Task dump for CPU 0:
[  725.670017] kworker/0:1     S ffff8800633abde8 13016   520      2 0x10080008
[  725.670017]  ffffffffb03027a8 ffff880a70f24017 ffffffffb043ef40 ffff88005ffea310
[  725.670017]  0000000000000000 dfffe90000000000 0000000000000000 1ffffffff63bcdeb
[  725.670017]  ffff88006be15030 ffffffffb1de6f58 ffffffffffffff10 ffffffffb0301237
[  725.670017] Call Trace:
[  725.670017]  [<ffffffffb03027a8>] ? retint_restore_args+0x13/0x13
[  725.670017]  [<ffffffffb0301237>] ? _raw_spin_unlock_irq+0x57/0x200
[  725.670017]  [<ffffffffb0301203>] ? _raw_spin_unlock_irq+0x23/0x200
[  725.670017]  [<ffffffffa04630cb>] ? worker_thread+0x15b/0x1680
[  725.670017]  [<ffffffffb02effef>] ? __schedule+0xf6f/0x2fc0
[  725.670017]  [<ffffffffa0462f70>] ? process_one_work+0x1650/0x1650
[  725.670017]  [<ffffffffa047ae12>] ? kthread+0x1f2/0x2b0
[  725.670017]  [<ffffffffa047ac20>] ? kthread_worker_fn+0x6a0/0x6a0
[  725.670017]  [<ffffffffb03018bc>] ? ret_from_fork+0x7c/0xb0
[  725.670017]  [<ffffffffa047ac20>] ? kthread_worker_fn+0x6a0/0x6a0


Thanks,
Sasha
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