diff options
author | Paul E. McKenney <paulmck@linux.ibm.com> | 2018-11-29 13:28:49 -0800 |
---|---|---|
committer | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-01-25 15:28:30 -0800 |
commit | 260e1e4fd826a8e47c8976efba6a54d62b4a57de (patch) | |
tree | c9e6ac47f789562966eed2eea94da1593440bc7f /kernel | |
parent | 892307266429f6439803f2735a59a4bc58a6ded4 (diff) |
rcu: Discard separate per-CPU callback counts
Back when there were multiple flavors of RCU, it was necessary to
separately count lazy and non-lazy callbacks for each CPU. These counts
were used in CONFIG_RCU_FAST_NO_HZ kernels to determine how long a newly
idle CPU should be allowed to sleep before handling its RCU callbacks.
But now that there is only one flavor, the callback counts for a given
CPU's sole rcu_data structure are the counts for that CPU.
This commit therefore removes the rcu_data structure's ->nonlazy_posted
and ->nonlazy_posted_snap fields, the rcu_idle_count_callbacks_posted()
and rcu_cpu_has_callbacks() functions, repurposes the rcu_data structure's
->all_lazy field to record the laziness state at the beginning of the
latest idle sojourn, and modifies CONFIG_RCU_FAST_NO_HZ RCU CPU stall
warnings accordingly.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/rcu/tree.c | 25 | ||||
-rw-r--r-- | kernel/rcu/tree.h | 6 | ||||
-rw-r--r-- | kernel/rcu/tree_plugin.h | 50 |
3 files changed, 13 insertions, 68 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e2bd42b2b563..e53a586b397b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2878,9 +2878,6 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func, int cpu, bool lazy) rcu_segcblist_init(&rdp->cblist); } rcu_segcblist_enqueue(&rdp->cblist, head, lazy); - if (!lazy) - rcu_idle_count_callbacks_posted(); - if (__is_kfree_rcu_offset((unsigned long)func)) trace_rcu_kfree_callback(rcu_state.name, head, (unsigned long)func, @@ -3111,28 +3108,6 @@ static int rcu_pending(void) } /* - * Return true if the specified CPU has any callback. If all_lazy is - * non-NULL, store an indication of whether all callbacks are lazy. - * (If there are no callbacks, all of them are deemed to be lazy.) - */ -static bool rcu_cpu_has_callbacks(bool *all_lazy) -{ - bool al = true; - bool hc = false; - struct rcu_data *rdp; - - rdp = this_cpu_ptr(&rcu_data); - if (!rcu_segcblist_empty(&rdp->cblist)) { - hc = true; - if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) - al = false; - } - if (all_lazy) - *all_lazy = al; - return hc; -} - -/* * Helper function for rcu_barrier() tracing. If tracing is disabled, * the compiler is expected to optimize this away. */ diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 50bb41cdc5fb..20feecbb0ab6 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -193,10 +193,7 @@ struct rcu_data { bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */ bool rcu_urgent_qs; /* GP old need light quiescent state. */ #ifdef CONFIG_RCU_FAST_NO_HZ - bool all_lazy; /* Are all CPU's CBs lazy? */ - unsigned long nonlazy_posted; /* # times non-lazy CB posted to CPU. */ - unsigned long nonlazy_posted_snap; - /* Nonlazy_posted snapshot. */ + bool all_lazy; /* All CPU's CBs lazy at idle start? */ unsigned long last_accelerate; /* Last jiffy CBs were accelerated. */ unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */ int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */ @@ -430,7 +427,6 @@ static void __init rcu_spawn_boost_kthreads(void); static void rcu_prepare_kthreads(int cpu); static void rcu_cleanup_after_idle(void); static void rcu_prepare_for_idle(void); -static void rcu_idle_count_callbacks_posted(void); static bool rcu_preempt_has_tasks(struct rcu_node *rnp); static bool rcu_preempt_need_deferred_qs(struct task_struct *t); static void rcu_preempt_deferred_qs(struct task_struct *t); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 43f3f2ee9d63..abd238c70900 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1474,7 +1474,7 @@ static void rcu_prepare_kthreads(int cpu) int rcu_needs_cpu(u64 basemono, u64 *nextevt) { *nextevt = KTIME_MAX; - return rcu_cpu_has_callbacks(NULL); + return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist); } /* @@ -1493,14 +1493,6 @@ static void rcu_prepare_for_idle(void) { } -/* - * Don't bother keeping a running count of the number of RCU callbacks - * posted because CONFIG_RCU_FAST_NO_HZ=n. - */ -static void rcu_idle_count_callbacks_posted(void) -{ -} - #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ /* @@ -1583,11 +1575,8 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) lockdep_assert_irqs_disabled(); - /* Snapshot to detect later posting of non-lazy callback. */ - rdp->nonlazy_posted_snap = rdp->nonlazy_posted; - /* If no callbacks, RCU doesn't need the CPU. */ - if (!rcu_cpu_has_callbacks(&rdp->all_lazy)) { + if (rcu_segcblist_empty(&rdp->cblist)) { *nextevt = KTIME_MAX; return 0; } @@ -1601,11 +1590,12 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) rdp->last_accelerate = jiffies; /* Request timer delay depending on laziness, and round. */ - if (!rdp->all_lazy) { + rdp->all_lazy = !rcu_segcblist_n_nonlazy_cbs(&rdp->cblist); + if (rdp->all_lazy) { + dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; + } else { dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - jiffies; - } else { - dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; } *nextevt = basemono + dj * TICK_NSEC; return 0; @@ -1635,7 +1625,7 @@ static void rcu_prepare_for_idle(void) /* Handle nohz enablement switches conservatively. */ tne = READ_ONCE(tick_nohz_active); if (tne != rdp->tick_nohz_enabled_snap) { - if (rcu_cpu_has_callbacks(NULL)) + if (!rcu_segcblist_empty(&rdp->cblist)) invoke_rcu_core(); /* force nohz to see update. */ rdp->tick_nohz_enabled_snap = tne; return; @@ -1648,10 +1638,8 @@ static void rcu_prepare_for_idle(void) * callbacks, invoke RCU core for the side-effect of recalculating * idle duration on re-entry to idle. */ - if (rdp->all_lazy && - rdp->nonlazy_posted != rdp->nonlazy_posted_snap) { + if (rdp->all_lazy && rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) { rdp->all_lazy = false; - rdp->nonlazy_posted_snap = rdp->nonlazy_posted; invoke_rcu_core(); return; } @@ -1687,19 +1675,6 @@ static void rcu_cleanup_after_idle(void) invoke_rcu_core(); } -/* - * Keep a running count of the number of non-lazy callbacks posted - * on this CPU. This running counter (which is never decremented) allows - * rcu_prepare_for_idle() to detect when something out of the idle loop - * posts a callback, even if an equal number of callbacks are invoked. - * Of course, callbacks should only be posted from within a trace event - * designed to be called from idle or from within RCU_NONIDLE(). - */ -static void rcu_idle_count_callbacks_posted(void) -{ - __this_cpu_add(rcu_data.nonlazy_posted, 1); -} - #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ #ifdef CONFIG_RCU_FAST_NO_HZ @@ -1707,13 +1682,12 @@ static void rcu_idle_count_callbacks_posted(void) static void print_cpu_stall_fast_no_hz(char *cp, int cpu) { struct rcu_data *rdp = &per_cpu(rcu_data, cpu); - unsigned long nlpd = rdp->nonlazy_posted - rdp->nonlazy_posted_snap; - sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", + sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c", rdp->last_accelerate & 0xffff, jiffies & 0xffff, - ulong2long(nlpd), - rdp->all_lazy ? 'L' : '.', - rdp->tick_nohz_enabled_snap ? '.' : 'D'); + ".l"[rdp->all_lazy], + ".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)], + ".D"[!rdp->tick_nohz_enabled_snap]); } #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ |