From: "Paul E. McKenney" <[email protected]>
> b. Maybe sysfs setting. Initially, this can be simple "on" and "off",
> exported with root-only access (like you have above). If more
> elaborate use cases appear, this might become the adminstrative
> override. The key point is that this needs to go through some
> sort of separate function (for example, via the KERNEL_ATTR_RW()
> macro) so that if it needs to change in the future, we can do
> the change easily.
I did not really envision the module param to be an application
interface, more like an administrative interface. For dynamically
requesting things on/off you probably want something like PM QoS which
does proper book keeping and consolidation but PM QoS for this feels a
bit overkill. But I do not think sysfs node is appropriate either for
an application interface. I guess module_param_cb() would also achieve
the goal of "doing something" upon parameter change. Anyway - below
the 0-perm module param + sysfs node version.
--Antti
Add a module parameter for always using expedited RCU primitives.
Signed-off-by: Antti P Miettinen <[email protected]>
---
kernel/ksysfs.c | 18 ++++++++++++++++++
kernel/rcu.h | 2 ++
kernel/rcupdate.c | 3 +++
kernel/rcutiny_plugin.h | 5 ++++-
kernel/rcutree.c | 10 ++++++++--
kernel/rcutree_plugin.h | 5 ++++-
kernel/srcu.c | 6 +++++-
7 files changed, 44 insertions(+), 5 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 4fb2376..744c117 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2221,7 +2221,10 @@ 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);
@@ -2242,7 +2245,10 @@ 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);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f921154..0e9ca8b 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);
diff --git a/kernel/srcu.c b/kernel/srcu.c
index 97c465e..d56873c 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -34,6 +34,8 @@
#include <linux/delay.h>
#include <linux/srcu.h>
+#include "rcu.h"
+
/*
* Initialize an rcu_batch structure to empty.
*/
@@ -464,7 +466,9 @@ 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);
--
1.7.4.1
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