linux-kernel - RE: [PATCH v4 4/4] rcu: Add RCU stall diagnosis information

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Date:   Tue, 8 Nov 2022 19:29:34 +0000
From:   "Elliott, Robert (Servers)" <elliott@....com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>,
        "paulmck@...nel.org" <paulmck@...nel.org>
CC:     Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        "Steven Rostedt" <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 4/4] rcu: Add RCU stall diagnosis information


> Maybe we should add another member to record jiffies.
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index b33165dba1ea745..6d9c876ea5c85a6 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -880,6 +880,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data
> *rdp)
>                         rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu);
>                         rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp-
> >cpu);
>                         rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu);
> +                       rsrp->jiffies = jiffies;
>                         rsrp->gp_seq = rdp->gp_seq;

Yes, that works:

[  252.139108] tcrypt: rcu testing - kernel_fpu_disable for rude 22 s
[  255.140204] rcu: INFO: rcu_preempt self-detected stall on CPU 39
[  255.146438] rcu:     CPU 39-....: (2995 ticks this GP) idle=5014/1/0x4000000000000000 softirq=2373/2374 fqs=751
[  255.156512] rcu:     CPU 39          hardirqs   softirqs           csw     system  cond_resched
[  255.165182] rcu:     CPU 39   count:        0          3             0                        0
[  255.173853] rcu:     CPU 39 cputime:        3          0                     1493               ==> 1530 (ms)
[  255.183746] rcu:     CPU 39 current: in_kernel_fpu_begin=1 preemptible=0
[  255.190407] rcu:     CPU 39 self-detected stall t=3051 jiffies g=18181 q=373 ncpus=56
[  255.198205] CPU: 39 PID: 2607 Comm: modprobe Not tainted 6.0.0+ #14
...
[  264.450164] rcu: INFO: rcu_preempt self-detected stall on CPU 39
[  264.456416] rcu:     CPU 39-...k.: (12000 ticks this GP) idle=5014/1/0x4000000000000000 softirq=2373/2374 fqs=3006
[  264.466690] rcu:     CPU 39          hardirqs   softirqs           csw     system  cond_resched
[  264.475390] rcu:     CPU 39   count:        0         21             0                        0
[  264.484092] rcu:     CPU 39 cputime:      328          0                     8982               ==> 9293 (ms)
[  264.494015] rcu:     CPU 39 current: in_kernel_fpu_begin=1 preemptible=0
[  264.500706] rcu:     CPU 39 self-detected stall t=12361 jiffies g=18181 q=601 ncpus=56
[  264.508619] CPU: 39 PID: 2607 Comm: modprobe Not tainted 6.0.0+ #14
...
[  273.760124] rcu: INFO: rcu_preempt self-detected stall on CPU 39
[  273.766376] rcu:     CPU 39-....: (21004 ticks this GP) idle=5014/1/0x4000000000000000 softirq=2373/2374 fqs=5262
[  273.776649] rcu:     CPU 39          hardirqs   softirqs           csw     system  cond_resched
[  273.785348] rcu:     CPU 39   count:        0         17             0                        0
[  273.794050] rcu:     CPU 39 cputime:      328          0                     8981               ==> 9293 (ms)
[  273.803971] rcu:     CPU 39 current: in_kernel_fpu_begin=1 preemptible=0
[  273.810660] rcu:     CPU 39 self-detected stall t=21671 jiffies g=18181 q=1112 ncpus=56
[  273.818659] CPU: 39 PID: 2607 Comm: modprobe Not tainted 6.0.0+ #14