aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/RCU/checklist.txt26
-rw-r--r--Documentation/RCU/lockdep.txt5
-rw-r--r--Documentation/RCU/rcubarrier.txt15
-rw-r--r--Documentation/RCU/stallwarn.txt33
-rw-r--r--Documentation/RCU/whatisRCU.txt4
-rw-r--r--Documentation/kernel-parameters.txt35
6 files changed, 85 insertions, 33 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 31ef8fe..79e789b8 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -217,9 +217,14 @@ over a rather long period of time, but improvements are always welcome!
whether the increased speed is worth it.
8. Although synchronize_rcu() is slower than is call_rcu(), it
- usually results in simpler code. So, unless update performance
- is critically important or the updaters cannot block,
- synchronize_rcu() should be used in preference to call_rcu().
+ usually results in simpler code. So, unless update performance is
+ critically important, the updaters cannot block, or the latency of
+ synchronize_rcu() is visible from userspace, synchronize_rcu()
+ should be used in preference to call_rcu(). Furthermore,
+ kfree_rcu() usually results in even simpler code than does
+ synchronize_rcu() without synchronize_rcu()'s multi-millisecond
+ latency. So please take advantage of kfree_rcu()'s "fire and
+ forget" memory-freeing capabilities where it applies.
An especially important property of the synchronize_rcu()
primitive is that it automatically self-limits: if grace periods
@@ -268,7 +273,8 @@ over a rather long period of time, but improvements are always welcome!
e. Periodically invoke synchronize_rcu(), permitting a limited
number of updates per grace period.
- The same cautions apply to call_rcu_bh() and call_rcu_sched().
+ The same cautions apply to call_rcu_bh(), call_rcu_sched(),
+ call_srcu(), and kfree_rcu().
9. All RCU list-traversal primitives, which include
rcu_dereference(), list_for_each_entry_rcu(), and
@@ -296,9 +302,9 @@ over a rather long period of time, but improvements are always welcome!
all currently executing rcu_read_lock()-protected RCU read-side
critical sections complete. It does -not- necessarily guarantee
that all currently running interrupts, NMIs, preempt_disable()
- code, or idle loops will complete. Therefore, if you do not have
- rcu_read_lock()-protected read-side critical sections, do -not-
- use synchronize_rcu().
+ code, or idle loops will complete. Therefore, if your
+ read-side critical sections are protected by something other
+ than rcu_read_lock(), do -not- use synchronize_rcu().
Similarly, disabling preemption is not an acceptable substitute
for rcu_read_lock(). Code that attempts to use preemption
@@ -401,9 +407,9 @@ over a rather long period of time, but improvements are always welcome!
read-side critical sections. It is the responsibility of the
RCU update-side primitives to deal with this.
-17. Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and
- the __rcu sparse checks to validate your RCU code. These
- can help find problems as follows:
+17. Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the
+ __rcu sparse checks (enabled by CONFIG_SPARSE_RCU_POINTER) to
+ validate your RCU code. These can help find problems as follows:
CONFIG_PROVE_RCU: check that accesses to RCU-protected data
structures are carried out under the proper RCU
diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt
index a102d4b..cd83d23 100644
--- a/Documentation/RCU/lockdep.txt
+++ b/Documentation/RCU/lockdep.txt
@@ -64,6 +64,11 @@ checking of rcu_dereference() primitives:
but retain the compiler constraints that prevent duplicating
or coalescsing. This is useful when when testing the
value of the pointer itself, for example, against NULL.
+ rcu_access_index(idx):
+ Return the value of the index and omit all barriers, but
+ retain the compiler constraints that prevent duplicating
+ or coalescsing. This is useful when when testing the
+ value of the index itself, for example, against -1.
The rcu_dereference_check() check expression can be any boolean
expression, but would normally include a lockdep expression. However,
diff --git a/Documentation/RCU/rcubarrier.txt b/Documentation/RCU/rcubarrier.txt
index 38428c1..2e319d1 100644
--- a/Documentation/RCU/rcubarrier.txt
+++ b/Documentation/RCU/rcubarrier.txt
@@ -79,7 +79,20 @@ complete. Pseudo-code using rcu_barrier() is as follows:
2. Execute rcu_barrier().
3. Allow the module to be unloaded.
-The rcutorture module makes use of rcu_barrier in its exit function
+There are also rcu_barrier_bh(), rcu_barrier_sched(), and srcu_barrier()
+functions for the other flavors of RCU, and you of course must match
+the flavor of rcu_barrier() with that of call_rcu(). If your module
+uses multiple flavors of call_rcu(), then it must also use multiple
+flavors of rcu_barrier() when unloading that module. For example, if
+it uses call_rcu_bh(), call_srcu() on srcu_struct_1, and call_srcu() on
+srcu_struct_2(), then the following three lines of code will be required
+when unloading:
+
+ 1 rcu_barrier_bh();
+ 2 srcu_barrier(&srcu_struct_1);
+ 3 srcu_barrier(&srcu_struct_2);
+
+The rcutorture module makes use of rcu_barrier() in its exit function
as follows:
1 static void
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 1927151..e38b8df 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
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 0cc7820..10df0b8 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -265,9 +265,9 @@ rcu_dereference()
rcu_read_lock();
p = rcu_dereference(head.next);
rcu_read_unlock();
- x = p->address;
+ x = p->address; /* BUG!!! */
rcu_read_lock();
- y = p->data;
+ y = p->data; /* BUG!!! */
rcu_read_unlock();
Holding a reference from one RCU read-side critical section
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4609e81..22303b2 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2461,9 +2461,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
In kernels built with CONFIG_RCU_NOCB_CPU=y, set
the specified list of CPUs to be no-callback CPUs.
Invocation of these CPUs' RCU callbacks will
- be offloaded to "rcuoN" kthreads created for
- that purpose. This reduces OS jitter on the
+ be offloaded to "rcuox/N" kthreads created for
+ that purpose, where "x" is "b" for RCU-bh, "p"
+ for RCU-preempt, and "s" for RCU-sched, and "N"
+ is the CPU number. This reduces OS jitter on the
offloaded CPUs, which can be useful for HPC and
+
real-time workloads. It can also improve energy
efficiency for asymmetric multiprocessors.
@@ -2487,6 +2490,17 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
leaf rcu_node structure. Useful for very large
systems.
+ rcutree.jiffies_till_first_fqs= [KNL,BOOT]
+ Set delay from grace-period initialization to
+ first attempt to force quiescent states.
+ Units are jiffies, minimum value is zero,
+ and maximum value is HZ.
+
+ rcutree.jiffies_till_next_fqs= [KNL,BOOT]
+ Set delay between subsequent attempts to force
+ quiescent states. Units are jiffies, minimum
+ value is one, and maximum value is HZ.
+
rcutree.qhimark= [KNL,BOOT]
Set threshold of queued
RCU callbacks over which batch limiting is disabled.
@@ -2501,16 +2515,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
Set timeout for RCU CPU stall warning messages.
- rcutree.jiffies_till_first_fqs= [KNL,BOOT]
- Set delay from grace-period initialization to
- first attempt to force quiescent states.
- Units are jiffies, minimum value is zero,
- and maximum value is HZ.
+ rcutree.rcu_idle_gp_delay= [KNL,BOOT]
+ Set wakeup interval for idle CPUs that have
+ RCU callbacks (RCU_FAST_NO_HZ=y).
- rcutree.jiffies_till_next_fqs= [KNL,BOOT]
- Set delay between subsequent attempts to force
- quiescent states. Units are jiffies, minimum
- value is one, and maximum value is HZ.
+ rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
+ Set wakeup interval for idle CPUs that have
+ only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
+ Lazy RCU callbacks are those which RCU can
+ prove do nothing more than free memory.
rcutorture.fqs_duration= [KNL,BOOT]
Set duration of force_quiescent_state bursts.