diff options
Diffstat (limited to 'Documentation/RCU/stallwarn.txt')
| -rw-r--r-- | Documentation/RCU/stallwarn.txt | 35 |
1 files changed, 25 insertions, 10 deletions
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index 1927151b386b..8e9359de1d28 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -92,14 +92,14 @@ If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set, more information is printed with the stall-warning message, for example: INFO: rcu_preempt detected stall on CPU - 0: (63959 ticks this GP) idle=241/3fffffffffffffff/0 + 0: (63959 ticks this GP) idle=241/3fffffffffffffff/0 softirq=82/543 (t=65000 jiffies) In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is printed: INFO: rcu_preempt detected stall on CPU - 0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 drain=0 . timer not pending + 0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D (t=65000 jiffies) The "(64628 ticks this GP)" indicates that this CPU has taken more @@ -116,13 +116,28 @@ number between the two "/"s is the value of the nesting, which will be a small positive number if in the idle loop and a very large positive number (as shown above) otherwise. -For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the CPU is -not in the process of trying to force itself into dyntick-idle state, the -"." indicates that the CPU has not given up forcing RCU into dyntick-idle -mode (it would be "H" otherwise), and the "timer not pending" indicates -that the CPU has not recently forced RCU into dyntick-idle mode (it -would otherwise indicate the number of microseconds remaining in this -forced state). +The "softirq=" portion of the message tracks the number of RCU softirq +handlers that the stalled CPU has executed. The number before the "/" +is the number that had executed since boot at the time that this CPU +last noted the beginning of a grace period, which might be the current +(stalled) grace period, or it might be some earlier grace period (for +example, if the CPU might have been in dyntick-idle mode for an extended +time period. The number after the "/" is the number that have executed +since boot until the current time. If this latter number stays constant +across repeated stall-warning messages, it is possible that RCU's softirq +handlers are no longer able to execute on this CPU. This can happen if +the stalled CPU is spinning with interrupts are disabled, or, in -rt +kernels, if a high-priority process is starving RCU's softirq handler. + +For CONFIG_RCU_FAST_NO_HZ kernels, the "last_accelerate:" prints the +low-order 16 bits (in hex) of the jiffies counter when this CPU last +invoked rcu_try_advance_all_cbs() from rcu_needs_cpu() or last invoked +rcu_accelerate_cbs() from rcu_prepare_for_idle(). The "nonlazy_posted:" +prints the number of non-lazy callbacks posted since the last call to +rcu_needs_cpu(). Finally, an "L" indicates that there are currently +no non-lazy callbacks ("." is printed otherwise, as shown above) and +"D" indicates that dyntick-idle processing is enabled ("." is printed +otherwise, for example, if disabled via the "nohz=" kernel boot parameter). Multiple Warnings From One Stall @@ -176,7 +191,7 @@ o A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that o A hardware or software issue shuts off the scheduler-clock interrupt on a CPU that is not in dyntick-idle mode. This problem really has happened, and seems to be most likely to - result in RCU CPU stall warnings for CONFIG_NO_HZ=n kernels. + result in RCU CPU stall warnings for CONFIG_NO_HZ_COMMON=n kernels. o A bug in the RCU implementation. |