* [PATCH tip/core/rcu 2/5] rcu: Update RCU_FAST_NO_HZ help text
2012-10-30 17:19 ` [PATCH tip/core/rcu 1/5] rcu: Remove rcu_switch() Paul E. McKenney
@ 2012-10-30 17:19 ` Paul E. McKenney
2012-10-30 17:19 ` [PATCH tip/core/rcu 3/5] rcu: Add a module parameter to force use of expedited RCU primitives Paul E. McKenney
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Paul E. McKenney @ 2012-10-30 17:19 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, patches, Paul E. McKenney, Paul E. McKenney
From: "Paul E. McKenney" <paul.mckenney@linaro.org>
The RCU_FAST_NO_HZ help text included a warning about overhead on large
systems, but that issue has since been resolved. The main remaining
issue with RCU_FAST_NO_HZ is increased real-time latency. This commit
therefore updates the help text accordingly.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
init/Kconfig | 15 +++++++--------
1 files changed, 7 insertions(+), 8 deletions(-)
diff --git a/init/Kconfig b/init/Kconfig
index 6fdd6e3..b63e798 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -582,14 +582,13 @@ config RCU_FAST_NO_HZ
depends on NO_HZ && SMP
default n
help
- This option causes RCU to attempt to accelerate grace periods
- in order to allow CPUs to enter dynticks-idle state more
- quickly. On the other hand, this option increases the overhead
- of the dynticks-idle checking, particularly on systems with
- large numbers of CPUs.
-
- Say Y if energy efficiency is critically important, particularly
- if you have relatively few CPUs.
+ This option causes RCU to attempt to accelerate grace periods in
+ order to allow CPUs to enter dynticks-idle state more quickly.
+ On the other hand, this option increases the overhead of the
+ dynticks-idle checking, thus degrading scheduling latency.
+
+ Say Y if energy efficiency is critically important, and you don't
+ care about real-time response.
Say N if you are unsure.
--
1.7.8
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH tip/core/rcu 3/5] rcu: Add a module parameter to force use of expedited RCU primitives
2012-10-30 17:19 ` [PATCH tip/core/rcu 1/5] rcu: Remove rcu_switch() Paul E. McKenney
2012-10-30 17:19 ` [PATCH tip/core/rcu 2/5] rcu: Update RCU_FAST_NO_HZ help text Paul E. McKenney
@ 2012-10-30 17:19 ` Paul E. McKenney
2012-10-30 17:19 ` [PATCH tip/core/rcu 4/5] rcu: Fix precedence error in cpu_needs_another_gp() Paul E. McKenney
2012-10-30 17:19 ` [PATCH tip/core/rcu 5/5] rcu: Wordsmith help text for RCU_USER_QS kernel parameter Paul E. McKenney
3 siblings, 0 replies; 6+ messages in thread
From: Paul E. McKenney @ 2012-10-30 17:19 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, patches, Antti P Miettinen, Antti P Miettinen,
Paul E. McKenney
From: Antti P Miettinen <ananaza@iki.fi>
There have been some embedded applications that would benefit from
use of expedited grace-period primitives. In some ways, this is
similar to synchronize_net() doing either a normal or an expedited
grace period depending on lock state, but with control outside of
the kernel.
This commit therefore adds rcu_expedited boot and sysfs parameters
that cause the kernel to substitute expedited primitives for the
normal grace-period primitives.
[ paulmck: Add trace/event/rcu.h to kernel/srcu.c to avoid build error.
Get rid of infinite loop through contention path.]
Signed-off-by: Antti P Miettinen <amiettinen@nvidia.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/ksysfs.c | 18 ++++++++++++++++++
kernel/rcu.h | 2 ++
kernel/rcupdate.c | 3 +++
kernel/rcutiny_plugin.h | 5 ++++-
kernel/rcutree.c | 12 +++++++++---
kernel/rcutree_plugin.h | 7 +++++--
kernel/srcu.c | 8 +++++++-
7 files changed, 48 insertions(+), 7 deletions(-)
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 4e316e1..8715a79 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -141,6 +141,23 @@ static ssize_t fscaps_show(struct kobject *kobj,
}
KERNEL_ATTR_RO(fscaps);
+int rcu_expedited;
+static ssize_t rcu_expedited_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%d\n", rcu_expedited);
+}
+static ssize_t rcu_expedited_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ if (kstrtoint(buf, 0, &rcu_expedited))
+ return -EINVAL;
+
+ return count;
+}
+KERNEL_ATTR_RW(rcu_expedited);
+
/*
* Make /sys/kernel/notes give the raw contents of our kernel .notes section.
*/
@@ -182,6 +199,7 @@ static struct attribute * kernel_attrs[] = {
&kexec_crash_size_attr.attr,
&vmcoreinfo_attr.attr,
#endif
+ &rcu_expedited_attr.attr,
NULL
};
diff --git a/kernel/rcu.h b/kernel/rcu.h
index 8ba99cd..20dfba5 100644
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -109,4 +109,6 @@ static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
}
}
+extern int rcu_expedited;
+
#endif /* __LINUX_RCU_H */
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 29ca1c6..a2cf761 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -46,12 +46,15 @@
#include <linux/export.h>
#include <linux/hardirq.h>
#include <linux/delay.h>
+#include <linux/module.h>
#define CREATE_TRACE_POINTS
#include <trace/events/rcu.h>
#include "rcu.h"
+module_param(rcu_expedited, int, 0);
+
#ifdef CONFIG_PREEMPT_RCU
/*
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 3d01902..f85016a 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -706,7 +706,10 @@ void synchronize_rcu(void)
return;
/* Once we get past the fastpath checks, same code as rcu_barrier(). */
- rcu_barrier();
+ if (rcu_expedited)
+ synchronize_rcu_expedited();
+ else
+ rcu_barrier();
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 74df86b..f9c17c3 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2224,7 +2224,10 @@ void synchronize_sched(void)
"Illegal synchronize_sched() in RCU-sched read-side critical section");
if (rcu_blocking_is_gp())
return;
- wait_rcu_gp(call_rcu_sched);
+ if (rcu_expedited)
+ synchronize_sched_expedited();
+ else
+ wait_rcu_gp(call_rcu_sched);
}
EXPORT_SYMBOL_GPL(synchronize_sched);
@@ -2245,7 +2248,10 @@ void synchronize_rcu_bh(void)
"Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
if (rcu_blocking_is_gp())
return;
- wait_rcu_gp(call_rcu_bh);
+ if (rcu_expedited)
+ synchronize_rcu_bh_expedited();
+ else
+ wait_rcu_gp(call_rcu_bh);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
@@ -2328,7 +2334,7 @@ void synchronize_sched_expedited(void)
if (trycount++ < 10) {
udelay(trycount * num_online_cpus());
} else {
- synchronize_sched();
+ wait_rcu_gp(call_rcu_sched);
return;
}
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f921154..c177ba0 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -679,7 +679,10 @@ void synchronize_rcu(void)
"Illegal synchronize_rcu() in RCU read-side critical section");
if (!rcu_scheduler_active)
return;
- wait_rcu_gp(call_rcu);
+ if (rcu_expedited)
+ synchronize_rcu_expedited();
+ else
+ wait_rcu_gp(call_rcu);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
@@ -831,7 +834,7 @@ void synchronize_rcu_expedited(void)
udelay(trycount * num_online_cpus());
} else {
put_online_cpus();
- synchronize_rcu();
+ wait_rcu_gp(call_rcu);
return;
}
}
diff --git a/kernel/srcu.c b/kernel/srcu.c
index 97c465e..de90740 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -34,6 +34,10 @@
#include <linux/delay.h>
#include <linux/srcu.h>
+#include <trace/events/rcu.h>
+
+#include "rcu.h"
+
/*
* Initialize an rcu_batch structure to empty.
*/
@@ -464,7 +468,9 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
*/
void synchronize_srcu(struct srcu_struct *sp)
{
- __synchronize_srcu(sp, SYNCHRONIZE_SRCU_TRYCOUNT);
+ __synchronize_srcu(sp, rcu_expedited
+ ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
+ : SYNCHRONIZE_SRCU_TRYCOUNT);
}
EXPORT_SYMBOL_GPL(synchronize_srcu);
--
1.7.8
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH tip/core/rcu 4/5] rcu: Fix precedence error in cpu_needs_another_gp()
2012-10-30 17:19 ` [PATCH tip/core/rcu 1/5] rcu: Remove rcu_switch() Paul E. McKenney
2012-10-30 17:19 ` [PATCH tip/core/rcu 2/5] rcu: Update RCU_FAST_NO_HZ help text Paul E. McKenney
2012-10-30 17:19 ` [PATCH tip/core/rcu 3/5] rcu: Add a module parameter to force use of expedited RCU primitives Paul E. McKenney
@ 2012-10-30 17:19 ` Paul E. McKenney
2012-10-30 17:19 ` [PATCH tip/core/rcu 5/5] rcu: Wordsmith help text for RCU_USER_QS kernel parameter Paul E. McKenney
3 siblings, 0 replies; 6+ messages in thread
From: Paul E. McKenney @ 2012-10-30 17:19 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, patches, Paul E. McKenney, Paul E. McKenney
From: "Paul E. McKenney" <paul.mckenney@linaro.org>
The fix introduced by a10d206e (rcu: Fix day-one dyntick-idle
stall-warning bug) has a C-language precedence error. It turns out
that this error is harmless in that the same result is computed for all
inputs, but the code is nevertheless a potential source of confusion.
This commit therefore introduces parentheses in order to force the
execution of the code to reflect the intent.
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f9c17c3..effd47a 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -313,7 +313,7 @@ static int
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
return *rdp->nxttail[RCU_DONE_TAIL +
- ACCESS_ONCE(rsp->completed) != rdp->completed] &&
+ (ACCESS_ONCE(rsp->completed) != rdp->completed)] &&
!rcu_gp_in_progress(rsp);
}
--
1.7.8
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH tip/core/rcu 5/5] rcu: Wordsmith help text for RCU_USER_QS kernel parameter
2012-10-30 17:19 ` [PATCH tip/core/rcu 1/5] rcu: Remove rcu_switch() Paul E. McKenney
` (2 preceding siblings ...)
2012-10-30 17:19 ` [PATCH tip/core/rcu 4/5] rcu: Fix precedence error in cpu_needs_another_gp() Paul E. McKenney
@ 2012-10-30 17:19 ` Paul E. McKenney
3 siblings, 0 replies; 6+ messages in thread
From: Paul E. McKenney @ 2012-10-30 17:19 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, patches, Paul Gortmaker, Paul E. McKenney
From: Paul Gortmaker <paul.gortmaker@windriver.com>
This commit adds a "try" missing from the end of the first paragraph
of the RCU_USER_QS help text.
[ paulmck: Also fix up the last paragraph a bit. ]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
init/Kconfig | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/init/Kconfig b/init/Kconfig
index b63e798..ec62139 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -494,11 +494,11 @@ config RCU_USER_QS
puts RCU in extended quiescent state when the CPU runs in
userspace. It means that when a CPU runs in userspace, it is
excluded from the global RCU state machine and thus doesn't
- to keep the timer tick on for RCU.
+ try to keep the timer tick on for RCU.
Unless you want to hack and help the development of the full
- tickless feature, you shouldn't enable this option. It adds
- unnecessary overhead.
+ tickless feature, you shouldn't enable this option. It also
+ adds unnecessary overhead.
If unsure say N
--
1.7.8
^ permalink raw reply [flat|nested] 6+ messages in thread