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Merge branches 'fixes.2015.07.22a' and 'initexp.2015.08.04a' into HEAD

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fixes.2015.07.22a: Miscellaneous fixes.
initexp.2015.08.04a: Initialization and expedited updates.
	(Single branch due to conflicts.)
This commit is contained in:
Paul E. McKenney
2015-08-04 08:40:58 -07:00
parent 9a54f98e34 af859beaab
commit 8ff4fbfd69
20 changed files with 435 additions and 476 deletions
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Documentation/RCU/stallwarn.txt
+19 -10
View File
@@ -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
Documentation/RCU/trace.txt
+10 -26
View File
@@ -237,42 +237,26 @@ o "ktl" is the low-order 16 bits (in hexadecimal) of the count of
The output of "cat rcu/rcu_preempt/rcuexp" looks as follows:
s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872
s=21872 wd0=0 wd1=0 wd2=0 wd3=5 n=0 enq=0 sc=21872
These fields are as follows:
o "s" is the starting sequence number.
o "s" is the sequence number, with an odd number indicating that
an expedited grace period is in progress.
o "d" is the ending sequence number. When the starting and ending
numbers differ, there is an expedited grace period in progress.
o "w" is the number of times that the sequence numbers have been
in danger of wrapping.
o "tf" is the number of times that contention has resulted in a
failure to begin an expedited grace period.
o "wd1" and "wd2" are the number of times that an attempt to
start an expedited grace period found that someone else had
completed an expedited grace period that satisfies the
o "wd0", "wd1", "wd2", and "wd3" are the number of times that an
attempt to start an expedited grace period found that someone
else had completed an expedited grace period that satisfies the
attempted request. "Our work is done."
o "n" is number of times that contention was so great that
the request was demoted from an expedited grace period to
a normal grace period.
o "n" is number of times that a concurrent CPU-hotplug operation
forced a fallback to a normal grace period.
o "enq" is the number of quiescent states still outstanding.
o "sc" is the number of times that the attempt to start a
new expedited grace period succeeded.
o "dt" is the number of times that we attempted to update
the "d" counter.
o "dl" is the number of times that we failed to update the "d"
counter.
o "dx" is the number of times that we succeeded in updating
the "d" counter.
The output of "cat rcu/rcu_preempt/rcugp" looks as follows: