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SubjectRe: [PATCH v8 0/6] rcu: Add RCU stall diagnosis information
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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

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