diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/stallwarn.rst | 56 |
1 files changed, 30 insertions, 26 deletions
diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst index c1e92dfef40d..ca7b7cd806a1 100644 --- a/Documentation/RCU/stallwarn.rst +++ b/Documentation/RCU/stallwarn.rst @@ -398,9 +398,9 @@ In kernels built with CONFIG_RCU_CPU_STALL_CPUTIME=y or booted with rcupdate.rcu_cpu_stall_cputime=1, the following additional information is supplied with each RCU CPU stall warning:: -rcu: hardirqs softirqs csw/system -rcu: number: 624 45 0 -rcu: cputime: 69 1 2425 ==> 2500(ms) + rcu: hardirqs softirqs csw/system + rcu: number: 624 45 0 + rcu: cputime: 69 1 2425 ==> 2500(ms) These statistics are collected during the sampling period. The values in row "number:" are the number of hard interrupts, number of soft @@ -412,22 +412,24 @@ in milliseconds. Because user-mode tasks normally do not cause RCU CPU stalls, these tasks are typically kernel tasks, which is why only the system CPU time are considered. -The sampling period is shown as follows: -:<------------first timeout---------->:<-----second timeout----->: -:<--half timeout-->:<--half timeout-->: : -: :<--first period-->: : -: :<-----------second sampling period---------->: -: : : : -: snapshot time point 1st-stall 2nd-stall +The sampling period is shown as follows:: + |<------------first timeout---------->|<-----second timeout----->| + |<--half timeout-->|<--half timeout-->| | + | |<--first period-->| | + | |<-----------second sampling period---------->| + | | | | + snapshot time point 1st-stall 2nd-stall The following describes four typical scenarios: -1. A CPU looping with interrupts disabled.:: +1. A CPU looping with interrupts disabled. - rcu: hardirqs softirqs csw/system - rcu: number: 0 0 0 - rcu: cputime: 0 0 0 ==> 2500(ms) + :: + + rcu: hardirqs softirqs csw/system + rcu: number: 0 0 0 + rcu: cputime: 0 0 0 ==> 2500(ms) Because interrupts have been disabled throughout the measurement interval, there are no interrupts and no context switches. @@ -440,11 +442,11 @@ The following describes four typical scenarios: This is similar to the previous example, but with non-zero number of and CPU time consumed by hard interrupts, along with non-zero CPU - time consumed by in-kernel execution.:: + time consumed by in-kernel execution:: - rcu: hardirqs softirqs csw/system - rcu: number: 624 0 0 - rcu: cputime: 49 0 2446 ==> 2500(ms) + rcu: hardirqs softirqs csw/system + rcu: number: 624 0 0 + rcu: cputime: 49 0 2446 ==> 2500(ms) The fact that there are zero softirqs gives a hint that these were disabled, perhaps via local_bh_disable(). It is of course possible @@ -454,20 +456,22 @@ The following describes four typical scenarios: 3. A CPU looping with preemption disabled. - Here, only the number of context switches is zero.:: + Here, only the number of context switches is zero:: - rcu: hardirqs softirqs csw/system - rcu: number: 624 45 0 - rcu: cputime: 69 1 2425 ==> 2500(ms) + rcu: hardirqs softirqs csw/system + rcu: number: 624 45 0 + rcu: cputime: 69 1 2425 ==> 2500(ms) This situation hints that the stalled CPU was looping with preemption disabled. -4. No looping, but massive hard and soft interrupts.:: +4. No looping, but massive hard and soft interrupts. + + :: - rcu: hardirqs softirqs csw/system - rcu: number: xx xx 0 - rcu: cputime: xx xx 0 ==> 2500(ms) + rcu: hardirqs softirqs csw/system + rcu: number: xx xx 0 + rcu: cputime: xx xx 0 ==> 2500(ms) Here, the number and CPU time of hard interrupts are all non-zero, but the number of context switches and the in-kernel CPU time consumed |