XXX I'm pretty sure I broke task-trace-rcu.
XXX trace_rcu_*() now gets an unconditional 0
Other than that, it seems like a fairly straight-forward replacement
of the RCU count with the context_tracking count.
Using context-tracking for this avoids having two (expensive) atomic
ops on the entry paths where one will do.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
include/linux/context_tracking.h | 6 ++
kernel/context_tracking.c | 14 +++++
kernel/rcu/tree.c | 101 +++++----------------------------------
kernel/rcu/tree.h | 1
4 files changed, 33 insertions(+), 89 deletions(-)
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -50,6 +50,9 @@ extern void context_tracking_user_exit(v
extern bool context_tracking_set_cpu_work(unsigned int cpu, unsigned int work);
+extern void context_tracking_idle(void);
+extern void context_tracking_online(void);
+
static inline void ct_user_enter(void)
{
if (context_tracking_enabled())
@@ -162,6 +165,9 @@ static __always_inline unsigned int __co
return 0;
}
+static inline void context_tracking_idle(void) { }
+static inline void context_tracking_online(void) { }
+
#endif /* !CONFIG_CONTEXT_TRACKING */
static __always_inline bool context_tracking_cpu_in_user(unsigned int cpu)
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -281,6 +281,20 @@ void noinstr __context_tracking_nmi_exit
ct_seq_nmi_exit(raw_cpu_ptr(&context_tracking));
}
+void context_tracking_online(void)
+{
+ struct context_tracking *ct = raw_cpu_ptr(&context_tracking);
+ unsigned int seq = atomic_read(&ct->seq);
+
+ if (__context_tracking_seq_in_user(seq))
+ atomic_add_return(CT_SEQ - CT_SEQ_USER, &ct->seq);
+}
+
+void context_tracking_idle(void)
+{
+ atomic_add_return(CT_SEQ, &raw_cpu_ptr(&context_tracking)->seq);
+}
+
void __init context_tracking_cpu_set(int cpu)
{
static __initdata bool initialized = false;
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -62,6 +62,7 @@
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/kasan.h>
+#include <linux/context_tracking.h>
#include "../time/tick-internal.h"
#include "tree.h"
@@ -77,7 +78,6 @@
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
.dynticks_nesting = 1,
.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
- .dynticks = ATOMIC_INIT(1),
#ifdef CONFIG_RCU_NOCB_CPU
.cblist.flags = SEGCBLIST_SOFTIRQ_ONLY,
#endif
@@ -252,56 +252,6 @@ void rcu_softirq_qs(void)
}
/*
- * Increment the current CPU's rcu_data structure's ->dynticks field
- * with ordering. Return the new value.
- */
-static noinline noinstr unsigned long rcu_dynticks_inc(int incby)
-{
- return arch_atomic_add_return(incby, this_cpu_ptr(&rcu_data.dynticks));
-}
-
-/*
- * Record entry into an extended quiescent state. This is only to be
- * called when not already in an extended quiescent state, that is,
- * RCU is watching prior to the call to this function and is no longer
- * watching upon return.
- */
-static noinstr void rcu_dynticks_eqs_enter(void)
-{
- int seq;
-
- /*
- * CPUs seeing atomic_add_return() must see prior RCU read-side
- * critical sections, and we also must force ordering with the
- * next idle sojourn.
- */
- rcu_dynticks_task_trace_enter(); // Before ->dynticks update!
- seq = rcu_dynticks_inc(1);
- // RCU is no longer watching. Better be in extended quiescent state!
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & 0x1));
-}
-
-/*
- * Record exit from an extended quiescent state. This is only to be
- * called from an extended quiescent state, that is, RCU is not watching
- * prior to the call to this function and is watching upon return.
- */
-static noinstr void rcu_dynticks_eqs_exit(void)
-{
- int seq;
-
- /*
- * CPUs seeing atomic_add_return() must see prior idle sojourns,
- * and we also must force ordering with the next RCU read-side
- * critical section.
- */
- seq = rcu_dynticks_inc(1);
- // RCU is now watching. Better not be in an extended quiescent state!
- rcu_dynticks_task_trace_exit(); // After ->dynticks update!
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & 0x1));
-}
-
-/*
* Reset the current CPU's ->dynticks counter to indicate that the
* newly onlined CPU is no longer in an extended quiescent state.
* This will either leave the counter unchanged, or increment it
@@ -313,11 +263,7 @@ static noinstr void rcu_dynticks_eqs_exi
*/
static void rcu_dynticks_eqs_online(void)
{
- struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
-
- if (atomic_read(&rdp->dynticks) & 0x1)
- return;
- rcu_dynticks_inc(1);
+ context_tracking_online();
}
/*
@@ -327,7 +273,7 @@ static void rcu_dynticks_eqs_online(void
*/
static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
{
- return !(atomic_read(this_cpu_ptr(&rcu_data.dynticks)) & 0x1);
+ return context_tracking_cpu_in_user(smp_processor_id());
}
/*
@@ -337,7 +283,7 @@ static __always_inline bool rcu_dynticks
static int rcu_dynticks_snap(struct rcu_data *rdp)
{
smp_mb(); // Fundamental RCU ordering guarantee.
- return atomic_read_acquire(&rdp->dynticks);
+ return __context_tracking_cpu_seq(rdp->cpu);
}
/*
@@ -346,7 +292,7 @@ static int rcu_dynticks_snap(struct rcu_
*/
static bool rcu_dynticks_in_eqs(int snap)
{
- return !(snap & 0x1);
+ return __context_tracking_seq_in_user(snap);
}
/* Return true if the specified CPU is currently idle from an RCU viewpoint. */
@@ -377,7 +323,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, i
int snap;
// If not quiescent, force back to earlier extended quiescent state.
- snap = atomic_read(&rdp->dynticks) & ~0x1;
+ snap = __context_tracking_cpu_seq(rdp->cpu) & ~0x7;
smp_rmb(); // Order ->dynticks and *vp reads.
if (READ_ONCE(*vp))
@@ -385,7 +331,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, i
smp_rmb(); // Order *vp read and ->dynticks re-read.
// If still in the same extended quiescent state, we are good!
- return snap == atomic_read(&rdp->dynticks);
+ return snap == __context_tracking_cpu_seq(rdp->cpu);
}
/*
@@ -401,12 +347,8 @@ bool rcu_dynticks_zero_in_eqs(int cpu, i
*/
notrace void rcu_momentary_dyntick_idle(void)
{
- int seq;
-
raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
- seq = rcu_dynticks_inc(2);
- /* It is illegal to call this from idle state. */
- WARN_ON_ONCE(!(seq & 0x1));
+ context_tracking_idle();
rcu_preempt_deferred_qs(current);
}
EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
@@ -622,18 +564,15 @@ static noinstr void rcu_eqs_enter(bool u
lockdep_assert_irqs_disabled();
instrumentation_begin();
- trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks));
+ trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, 0);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
rcu_prepare_for_idle();
rcu_preempt_deferred_qs(current);
- // instrumentation for the noinstr rcu_dynticks_eqs_enter()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
instrumentation_end();
WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
// RCU is watching here ...
- rcu_dynticks_eqs_enter();
// ... but is no longer watching here.
rcu_dynticks_task_enter();
}
@@ -756,8 +695,7 @@ noinstr void rcu_nmi_exit(void)
* leave it in non-RCU-idle state.
*/
if (rdp->dynticks_nmi_nesting != 1) {
- trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
- atomic_read(&rdp->dynticks));
+ trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, 0);
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
rdp->dynticks_nmi_nesting - 2);
instrumentation_end();
@@ -765,18 +703,15 @@ noinstr void rcu_nmi_exit(void)
}
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
- trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
+ trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, 0);
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
if (!in_nmi())
rcu_prepare_for_idle();
- // instrumentation for the noinstr rcu_dynticks_eqs_enter()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
instrumentation_end();
// RCU is watching here ...
- rcu_dynticks_eqs_enter();
// ... but is no longer watching here.
if (!in_nmi())
@@ -865,15 +800,11 @@ static void noinstr rcu_eqs_exit(bool us
}
rcu_dynticks_task_exit();
// RCU is not watching here ...
- rcu_dynticks_eqs_exit();
// ... but is watching here.
instrumentation_begin();
- // instrumentation for the noinstr rcu_dynticks_eqs_exit()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
-
rcu_cleanup_after_idle();
- trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks));
+ trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, 0);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
WRITE_ONCE(rdp->dynticks_nesting, 1);
WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
@@ -1011,7 +942,6 @@ noinstr void rcu_nmi_enter(void)
rcu_dynticks_task_exit();
// RCU is not watching here ...
- rcu_dynticks_eqs_exit();
// ... but is watching here.
if (!in_nmi()) {
@@ -1021,11 +951,6 @@ noinstr void rcu_nmi_enter(void)
}
instrumentation_begin();
- // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
- instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks));
- // instrumentation for the noinstr rcu_dynticks_eqs_exit()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
-
incby = 1;
} else if (!in_nmi()) {
instrumentation_begin();
@@ -1036,7 +961,7 @@ noinstr void rcu_nmi_enter(void)
trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
rdp->dynticks_nmi_nesting,
- rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
+ rdp->dynticks_nmi_nesting + incby, 0);
instrumentation_end();
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
rdp->dynticks_nmi_nesting + incby);
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -184,7 +184,6 @@ struct rcu_data {
int dynticks_snap; /* Per-GP tracking for dynticks. */
long dynticks_nesting; /* Track process nesting level. */
long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */
- atomic_t dynticks; /* Even value for idle, else odd. */
bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */
bool rcu_urgent_qs; /* GP old need light quiescent state. */
bool rcu_forced_tick; /* Forced tick to provide QS. */
