rcu: Add RCU stall diagnosis information #18
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Similar to kstat_cpu_irqs_sum(), it counts the sum of all software interrupts on a specified CPU. Signed-off-by: Zhen Lei <[email protected]>
Returns the number of context switches on the specified CPU, which can be used to diagnose rcu stall. Signed-off-by: Zhen Lei <[email protected]>
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. For example: rcu: INFO: rcu_preempt self-detected stall on CPU rcu: 0-....: (1250 ticks this GP) <omitted> rcu: hardirqs softirqs csw/system rcu: number: 624 45 0 rcu: cputime: 69 1 2425 ==> 2500(ms) The example above shows that the number of hard and soft interrupts is small, there is zero context switching, and the system takes up a lot of time. We can quickly conclude that the current task is infinitely looped with preempt_disable(). The impact on system performance is negligible because snapshot is recorded only one time after 1/2 CPU stall timeout. Signed-off-by: Zhen Lei <[email protected]>
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Pull request for series with
subject: rcu: Add RCU stall diagnosis information
version: 1
url: https://patchwork.kernel.org/project/rcu/list/?series=685780