On Tue 2015-09-08 12:59:15, Paul E. McKenney wrote: > On Mon, Sep 07, 2015 at 04:58:27PM +0200, Petr Mladek wrote: > > On Fri 2015-09-04 16:24:22, Paul E. McKenney wrote: > > > On Fri, Sep 04, 2015 at 02:11:29PM +0200, Petr Mladek wrote: [...]
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index 69ab7ce2cf7b..04234936d897 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -1949,16 +1949,15 @@ 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) > > > { > > > - 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 (rsp->gp_state == RCU_SAVE_DYNTICK) { > > > > This will never happen because rcu_gp_kthread() modifies rsp->gp_state > > many times. The last value before calling rcu_gp_fqs() is > > RCU_GP_DOING_FQS. > > > > I think about passing this information via a separate bool. > > > > [...] > > > > > diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h > > > index d5f58e717c8b..9faad70a8246 100644 > > > --- a/kernel/rcu/tree.h > > > +++ b/kernel/rcu/tree.h > > > @@ -417,12 +417,11 @@ struct rcu_data { > > > struct rcu_state *rsp; > > > }; > > > > > > -/* Values for fqs_state field in struct rcu_state. */ > > > +/* Values for gp_state field in struct rcu_state. */ > > > #define RCU_GP_IDLE 0 /* No grace period in progress. > > > */ > > > > This value seems to be used instead of the new RCU_GP_WAIT_INIT. > > > > > #define RCU_GP_INIT 1 /* Grace period being > > > #initialized. */ > > > > This value is unused. > > > > > #define RCU_SAVE_DYNTICK 2 /* Need to scan dyntick > > > #state. */ > > > > This one is not longer preserved when merged with the other state. > > > > > #define RCU_FORCE_QS 3 /* Need to force quiescent > > > #state. */ > > > > The meaning of this one is strange. If I get it correctly, > > it is set after the state was forced. But the comment suggests > > that it is before. > > > > By other words, these states seems to get obsoleted by > > > > /* Values for rcu_state structure's gp_flags field. */ > > #define RCU_GP_WAIT_INIT 0 /* Initial state. */ > > #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. */ > > #define RCU_GP_DOING_FQS 4 /* Wait done for force-quiescent-state time. */ > > #define RCU_GP_CLEANUP 5 /* Grace-period cleanup started. */ > > #define RCU_GP_CLEANED 6 /* Grace-period cleanup complete. */ > > > > > > Please, find below your commit updated with my ideas: > > > > + used bool save_dyntick instead of RCU_SAVE_DYNTICK > > and RCU_FORCE_QS states > > + rename RCU_GP_WAIT_INIT -> RCU_GP_IDLE > > + remove all the obsolete states > > > > I am sorry if I handled "Signed-off-by" flags a wrong way. It is > > basically your patch with few small updates from me. I am not sure > > what is the right process in this case. Feel free to use Reviewed-by > > instead of Signed-off-by with my name. > > > > Well, I guess that this is not the final state ;-) > > Good points, but perhaps an easier solution would be to have a > "firsttime" argument to rcu_gp_fqs() that said whether or not this > was the first call to rcu_gp_fqs() during the current grace period. > If this is the first call, then take the "if" branch that passes > dyntick_save_progress_counter() to force_qs_rnp(), otherwise take the > other branch. This seems to be the most elegant solution at the moment. > But I am not generating the patch today, just flew across the Pacific > yesterday. ;-) Please, find below the updated patch where I used the first_time parameter. Again, I am not sure about the commit person and Signed-off-by tags. Many parts of the patch are yours. Feel free to update them. >From 7d7f2ee97a451f5cb055901a3bf22fec23a53bff Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> Date: Fri, 4 Sep 2015 16:24:22 -0700 Subject: [PATCH] rcu: Finish folding ->fqs_state into ->gp_state Commit commit 4cdfc175c25c89ee ("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 had one side effect. It was used to decide whether to collect dyntick-idle snapshots. For this purpose, we add a boolean variable into the kthread. Reported-by: Petr Mladek <pmla...@suse.com> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> Signed-off-by: Petr Mladek <pmla...@suse.com> --- kernel/rcu/tree.c | 18 ++++++++---------- kernel/rcu/tree.h | 14 +++----------- kernel/rcu/tree_trace.c | 2 +- 3 files changed, 12 insertions(+), 22 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 9f75f25cc5d9..5413d87a67c6 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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), \ @@ -1927,16 +1927,15 @@ 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; @@ -1945,7 +1944,6 @@ 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; @@ -1959,7 +1957,6 @@ 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; } /* @@ -2023,7 +2020,7 @@ 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; @@ -2041,7 +2038,7 @@ 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; @@ -2073,7 +2070,7 @@ 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; @@ -2101,7 +2098,8 @@ 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")); diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 2e991f8361e4..de370b611837 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -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 @@ -469,9 +462,8 @@ 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. */ @@ -539,7 +531,7 @@ 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. */ diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c index 6fc4c5ff3bb5..1d61f5ba4641 100644 --- a/kernel/rcu/tree_trace.c +++ b/kernel/rcu/tree_trace.c @@ -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", -- 1.8.5.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/