On Wed, Nov 09, 2022 at 07:59:01AM -0800, Paul E. McKenney wrote: > On Wed, Nov 09, 2022 at 04:26:21PM +0100, Frederic Weisbecker wrote: > > Hi Zhen Lei, > > > > On Wed, Nov 09, 2022 at 05:37:36PM +0800, Zhen Lei wrote: > > > 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. > > > > That looks useful but I have to ask: what does it bring that the softlockup > > and hardlockup watchdog can not already solve? > > This is a good point. One possible benefit is putting the needed information > in one spot, for example, in cases where the soft/hard lockup timeouts are > significantly different than the RCU CPU stall warning timeout. Arguably, the hardlockup/softlockup detectors usually trigger after RCU stall, unless all CPUs are caught into a hardlockup, in which case only the hardlockup detector has a chance. Anyway I would say that in this case just lower the delay for the lockup detectors to consider the situation is a lockup? Thanks. > > Thoughts? > > Thanx, Paul > > > Thanks. > > > > > > > > Zhen Lei (2): > > > rcu: Add RCU stall diagnosis information > > > doc: Document CONFIG_RCU_CPU_STALL_CPUTIME=y stall information > > > > > > Documentation/RCU/stallwarn.rst | 88 +++++++++++++++++++ > > > .../admin-guide/kernel-parameters.txt | 6 ++ > > > kernel/rcu/Kconfig.debug | 11 +++ > > > kernel/rcu/rcu.h | 1 + > > > kernel/rcu/tree.c | 17 ++++ > > > kernel/rcu/tree.h | 19 ++++ > > > kernel/rcu/tree_stall.h | 29 ++++++ > > > kernel/rcu/update.c | 2 + > > > 8 files changed, 173 insertions(+) > > > > > > -- > > > 2.25.1 > > >
