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rcu: Finish folding ->fqs_state into ->gp_state

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Commit commit 4cdfc175c2 ("rcu: Move quiescent-state forcing
into kthread") started the process of folding the old ->fqs_state into
->gp_state, but did not complete it.  This situation does not cause
any malfunction, but can result in extremely confusing trace output.
This commit completes this task of eliminating ->fqs_state in favor
of ->gp_state.

The old ->fqs_state was also used to decide when to collect dyntick-idle
snapshots.  For this purpose, we add a boolean variable into the kthread,
which is set on the first call to rcu_gp_fqs() for a given grace period
and clear otherwise.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Petr Mladek 2015-09-09 12:09:49 -07:00 committed by Paul E. McKenney
parent 49f5903b47
commit 77f81fe08e
3 changed files with 12 additions and 22 deletions
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18
kernel/rcu/tree.c
View file

@ -98,7 +98,7 @@ struct rcu_state sname##_state = { \
.level = { &sname##_state.node[0] }, \
.rda = &sname##_data, \
.call = cr, \
.fqs_state = RCU_GP_IDLE, \
.gp_state = RCU_GP_IDLE, \
.gpnum = 0UL - 300UL, \
.completed = 0UL - 300UL, \
.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
@ -1936,16 +1936,15 @@ static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
/*
* Do one round of quiescent-state forcing.
*/
static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
{
int fqs_state = fqs_state_in;
bool isidle = false;
unsigned long maxj;
struct rcu_node *rnp = rcu_get_root(rsp);
WRITE_ONCE(rsp->gp_activity, jiffies);
rsp->n_force_qs++;
if (fqs_state == RCU_SAVE_DYNTICK) {
if (first_time) {
/* Collect dyntick-idle snapshots. */
if (is_sysidle_rcu_state(rsp)) {
isidle = true;
@ -1954,7 +1953,6 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
force_qs_rnp(rsp, dyntick_save_progress_counter,
&isidle, &maxj);
rcu_sysidle_report_gp(rsp, isidle, maxj);
fqs_state = RCU_FORCE_QS;
} else {
/* Handle dyntick-idle and offline CPUs. */
isidle = true;
@ -1968,7 +1966,6 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
raw_spin_unlock_irq(&rnp->lock);
}
return fqs_state;
}
/*
@ -2032,7 +2029,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
/* Declare grace period done. */
WRITE_ONCE(rsp->completed, rsp->gpnum);
trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
rsp->fqs_state = RCU_GP_IDLE;
rsp->gp_state = RCU_GP_IDLE;
rdp = this_cpu_ptr(rsp->rda);
/* Advance CBs to reduce false positives below. */
needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
@ -2050,7 +2047,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
*/
static int __noreturn rcu_gp_kthread(void *arg)
{
int fqs_state;
bool first_gp_fqs;
int gf;
unsigned long j;
int ret;
@ -2082,7 +2079,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
}
/* Handle quiescent-state forcing. */
fqs_state = RCU_SAVE_DYNTICK;
first_gp_fqs = true;
j = jiffies_till_first_fqs;
if (j > HZ) {
j = HZ;
@ -2110,7 +2107,8 @@ static int __noreturn rcu_gp_kthread(void *arg)
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsstart"));
fqs_state = rcu_gp_fqs(rsp, fqs_state);
rcu_gp_fqs(rsp, first_gp_fqs);
first_gp_fqs = false;
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsend"));

14
kernel/rcu/tree.h
View file

@ -412,13 +412,6 @@ struct rcu_data {
struct rcu_state *rsp;
};
/* Values for fqs_state field in struct rcu_state. */
#define RCU_GP_IDLE 0 /* No grace period in progress. */
#define RCU_GP_INIT 1 /* Grace period being initialized. */
#define RCU_SAVE_DYNTICK 2 /* Need to scan dyntick state. */
#define RCU_FORCE_QS 3 /* Need to force quiescent state. */
#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
/* Values for nocb_defer_wakeup field in struct rcu_data. */
#define RCU_NOGP_WAKE_NOT 0
#define RCU_NOGP_WAKE 1
@ -468,9 +461,8 @@ struct rcu_state {
/* The following fields are guarded by the root rcu_node's lock. */
u8 fqs_state ____cacheline_internodealigned_in_smp;
/* Force QS state. */
u8 boost; /* Subject to priority boost. */
u8 boost ____cacheline_internodealigned_in_smp;
/* Subject to priority boost. */
unsigned long gpnum; /* Current gp number. */
unsigned long completed; /* # of last completed gp. */
struct task_struct *gp_kthread; /* Task for grace periods. */
@ -538,7 +530,7 @@ struct rcu_state {
#define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */
/* Values for rcu_state structure's gp_flags field. */
#define RCU_GP_WAIT_INIT 0 /* Initial state. */
#define RCU_GP_IDLE 0 /* Initial state and no GP in progress. */
#define RCU_GP_WAIT_GPS 1 /* Wait for grace-period start. */
#define RCU_GP_DONE_GPS 2 /* Wait done for grace-period start. */
#define RCU_GP_WAIT_FQS 3 /* Wait for force-quiescent-state time. */

2
kernel/rcu/tree_trace.c
View file

@ -268,7 +268,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
gpnum = rsp->gpnum;
seq_printf(m, "c=%ld g=%ld s=%d jfq=%ld j=%x ",
ulong2long(rsp->completed), ulong2long(gpnum),
rsp->fqs_state,
rsp->gp_state,
(long)(rsp->jiffies_force_qs - jiffies),
(int)(jiffies & 0xffff));
seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",