linux-kernel - Re: [PATCH v8 0/6] rcu: Add RCU stall diagnosis information

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Date:   Tue, 22 Nov 2022 10:14:04 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     <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>,
        <linux-kernel@...r.kernel.org>, Robert Elliott <elliott@....com>
Subject: Re: [PATCH v8 0/6] rcu: Add RCU stall diagnosis information



On 2022/11/22 6:29, Paul E. McKenney wrote:
> On Sat, Nov 19, 2022 at 05:25:02PM +0800, Zhen Lei wrote:
>> v7 --> v8:
>> 1. Change call jiffies64_to_msecs() to call jiffies_to_msecs().
>> 2. Mention that rcupdate.rcu_cpu_stall_cputime overrides
>>    CONFIG_RCU_CPU_STALL_CPUTIME behaviour in the Kconfig help text.
>> 3. Fix a make htmldocs warning, change "|...|" to ":...:".
>>
>> v6 --> v7:
>> 1. Use kcpustat_field() to obtain the cputime.
>> 2. Make the output start with "\t" to match other related prints.
>> 3. Aligns the output of the last line of RCU stall.
>>
>> v5 --> v6:
>> 1. When there are more than two continuous RCU stallings, correctly handle the
>>    value of the second and subsequent sampling periods. Update comments and
>>    document.
>>    Thanks to Elliott, Robert for the test.
>> 2. Change "rcu stall" to "RCU stall".
>>
>> v4 --> v5:
>> 1. Resolve a git am conflict. No code change.
>>
>> v3 --> v4:
>> 1. Rename rcu_cpu_stall_deep_debug to rcu_cpu_stall_cputime.
>>
>> v2 --> v3:
>> 1. Fix the return type of kstat_cpu_irqs_sum()
>> 2. Add Kconfig option CONFIG_RCU_CPU_STALL_DEEP_DEBUG and boot parameter
>>    rcupdate.rcu_cpu_stall_deep_debug.
>> 3. Add comments and normalize local variable name
>>
>> v1 --> v2:
>> 1. Fixed a bug in the code. If the rcu stall is detected by another CPU,
>>    kcpustat_this_cpu cannot be used.
>> @@ -451,7 +451,7 @@ static void print_cpu_stat_info(int cpu)
>>         if (r->gp_seq != rdp->gp_seq)
>>                 return;
>>
>> -       cpustat = kcpustat_this_cpu->cpustat;
>> +       cpustat = kcpustat_cpu(cpu).cpustat;
>> 2. Move the start point of statistics from rcu_stall_kick_kthreads() to
>>    rcu_implicit_dynticks_qs(), removing the dependency on irq_work.
>>
>> v1:
>> In some extreme cases, such as the I/O pressure test, the CPU usage may
>> be 100%, causing RCU stall. In this case, the printed information about
>> current is not useful. Displays the number and usage of hard interrupts,
>> soft interrupts, and context switches that are generated within half of
>> the CPU stall timeout, can help us make a general judgment. In other
>> cases, we can preliminarily determine whether an infinite loop occurs
>> when local_irq, local_bh or preempt is disabled.
> 
> Queued for further review and testing, thank you!
> 
> I did the usual wordsmithing, so please check to see if I messed
> something up.

Thanks for your help.

Sorry, I think I missed a word in the commit message of patch 5/6.

This commit documents the additional RCU CPU stall warning output produced
- by kernels built with CONFIG_RCU_CPU_STALL_CPUTIME=y.
+ by kernels built with CONFIG_RCU_CPU_STALL_CPUTIME=y or booted with
+ rcupdate.rcu_cpu_stall_cputime=1.

> 
> 							Thanx, Paul
> 
>> Zhen Lei (6):
>>   genirq: Fix the return type of kstat_cpu_irqs_sum()
>>   sched: Add helper kstat_cpu_softirqs_sum()
>>   sched: Add helper nr_context_switches_cpu()
>>   rcu: Add RCU stall diagnosis information
>>   doc: Document CONFIG_RCU_CPU_STALL_CPUTIME=y stall information
>>   rcu: Align the output of RCU stall
>>
>>  Documentation/RCU/stallwarn.rst               | 88 +++++++++++++++++++
>>  .../admin-guide/kernel-parameters.txt         |  6 ++
>>  include/linux/kernel_stat.h                   | 14 ++-
>>  kernel/rcu/Kconfig.debug                      | 13 +++
>>  kernel/rcu/rcu.h                              |  1 +
>>  kernel/rcu/tree.c                             | 18 ++++
>>  kernel/rcu/tree.h                             | 19 ++++
>>  kernel/rcu/tree_stall.h                       | 35 +++++++-
>>  kernel/rcu/update.c                           |  2 +
>>  kernel/sched/core.c                           |  5 ++
>>  10 files changed, 198 insertions(+), 3 deletions(-)
>>
>> -- 
>> 2.25.1
>>
> .
> 

-- 
Regards,
  Zhen Lei