These changes are the raw update to linux-4.4.6-rt14. Kernel sources

[kvmfornfv.git] / kernel / Documentation / RCU / stallwarn.txt

diff --git a/kernel/Documentation/RCU/stallwarn.txt b/kernel/Documentation/RCU/stallwarn.txt
index b57c0c1..0f7fb42 100644 (file)
--- a/kernel/Documentation/RCU/stallwarn.txt
+++ b/kernel/Documentation/RCU/stallwarn.txt
@@ -26,12 +26,6 @@ CONFIG_RCU_CPU_STALL_TIMEOUT
        Stall-warning messages may be enabled and disabled completely via
        /sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.
 
-CONFIG_RCU_CPU_STALL_INFO
-
-       This kernel configuration parameter causes the stall warning to
-       print out additional per-CPU diagnostic information, including
-       information on scheduling-clock ticks and RCU's idle-CPU tracking.
-
 RCU_STALL_DELAY_DELTA
 
        Although the lockdep facility is extremely useful, it does add
@@ -101,15 +95,13 @@ interact.  Please note that it is not possible to entirely eliminate this
 sort of false positive without resorting to things like stop_machine(),
 which is overkill for this sort of problem.
 
-If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set,
-more information is printed with the stall-warning message, for example:
+Recent kernels will print a long form of the stall-warning message:
 
        INFO: rcu_preempt detected stall on CPU
        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:
+In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed:
 
        INFO: rcu_preempt detected stall on CPU
        0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D
@@ -171,6 +163,23 @@ message will be about three times the interval between the beginning
 of the stall and the first message.
 
 
+Stall Warnings for Expedited Grace Periods
+
+If an expedited grace period detects a stall, it will place a message
+like the following in dmesg:
+
+       INFO: rcu_sched detected expedited stalls on CPUs: { 1 2 6 } 26009 jiffies s: 1043
+
+This indicates that CPUs 1, 2, and 6 have failed to respond to a
+reschedule IPI, that the expedited grace period has been going on for
+26,009 jiffies, and that the expedited grace-period sequence counter is
+1043.  The fact that this last value is odd indicates that an expedited
+grace period is in flight.
+
+It is entirely possible to see stall warnings from normal and from
+expedited grace periods at about the same time from the same run.
+
+
 What Causes RCU CPU Stall Warnings?
 
 So your kernel printed an RCU CPU stall warning.  The next question is
@@ -196,6 +205,13 @@ o  For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the
        behavior, you might need to replace some of the cond_resched()
        calls with calls to cond_resched_rcu_qs().
 
+o      Booting Linux using a console connection that is too slow to
+       keep up with the boot-time console-message rate.  For example,
+       a 115Kbaud serial console can be -way- too slow to keep up
+       with boot-time message rates, and will frequently result in
+       RCU CPU stall warning messages.  Especially if you have added
+       debug printk()s.
+
 o      Anything that prevents RCU's grace-period kthreads from running.
        This can result in the "All QSes seen" console-log message.
        This message will include information on when the kthread last