On Sat, Nov 05, 2022 at 03:03:14PM +0800, Leizhen (ThunderTown) wrote: > On 2022/11/5 9:58, Elliott, Robert (Servers) wrote: [ . . . ] > >> +int rcu_cpu_stall_cputime __read_mostly = > >> IS_ENABLED(CONFIG_RCU_CPU_STALL_CPUTIME); > > > > As a config option and module parameter, adding some more > > instrumentation overhead might be worthwhile for other > > likely causes of rcu stalls. > > > > For example, if enabled, have these functions (if available > > on the architecture) maintain a per-CPU running count of > > their invocations, which also cause the CPU to be unavailable > > for rcu: > > - kernel_fpu_begin() calls - FPU/SIMD context preservation, > > which also calls preempt_disable() > > - preempt_disable() calls - scheduler context switches disabled > > - local_irq_save() calls - interrupts disabled > > - cond_resched() calls - lack of these is a problem > > > > For kernel_fpu_begin and preempt_disable, knowing if it is > > currently blocked for those reasons is probably the most > > helpful. > > These instructions is already in Documentation/RCU/stallwarn.rst Excellent point -- this document also needs to be updated with this new information. I have pulled in your four patches as noted in my previous email. They are on the -rcu tree's "dev" branch. Could you please send a patch containing an initial update to stallwarn.rst? The main thing I need is your perspective on how each field is used. Thanx, Paul
