diff options
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 9 | ||||
| -rw-r--r-- | include/linux/srcutree.h | 2 | ||||
| -rw-r--r-- | kernel/rcu/srcutree.c | 107 |
3 files changed, 94 insertions, 24 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 1f1fcac7777d..177e688768c0 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5616,6 +5616,7 @@ 0: Never. 1: At init_srcu_struct() time. 2: When rcutorture decides to. + 0x1X: Above plus if high contention. Either way, the srcu_node tree will be sized based on the actual runtime number of CPUs (nr_cpu_ids) @@ -5638,6 +5639,14 @@ expediting. Set to zero to disable automatic expediting. + srcutree.small_contention_lim [KNL] + Specifies the number of update-side contention + events per jiffy will be tolerated before + initiating a conversion of an srcu_struct + structure to big form. Note that the value of + srcutree.convert_to_big must have the 0x10 bit + set for contention-based conversions to occur. + ssbd= [ARM64,HW] Speculative Store Bypass Disable control diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 44bd204498a1..1b9ff4ed37e4 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -72,6 +72,8 @@ struct srcu_struct { unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */ + unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */ + unsigned long srcu_n_lock_retries; /* Contention events in current interval. */ struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ bool sda_is_static; /* May ->sda be passed to free_percpu()? */ unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */ diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index c9460374d437..0bc6a0a3edee 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -41,13 +41,29 @@ module_param(counter_wrap_check, ulong, 0444); /* * Control conversion to SRCU_SIZE_BIG: - * 0: Don't convert at all (default). - * 1: Convert at init_srcu_struct() time. - * 2: Convert when rcutorture invokes srcu_torture_stats_print(). + * 0: Don't convert at all (default). + * 1: Convert at init_srcu_struct() time. + * 2: Convert when rcutorture invokes srcu_torture_stats_print(). + * 3: Decide at boot time based on system shape. + * 0x1x: Convert when excessive contention encountered. */ -static int convert_to_big; +#define SRCU_SIZING_NONE 0 +#define SRCU_SIZING_INIT 1 +#define SRCU_SIZING_TORTURE 2 +#define SRCU_SIZING_AUTO 3 +#define SRCU_SIZING_CONTEND 0x10 +#define SRCU_SIZING_IS(x) ((convert_to_big & ~SRCU_SIZING_CONTEND) == x) +#define SRCU_SIZING_IS_NONE() (SRCU_SIZING_IS(SRCU_SIZING_NONE)) +#define SRCU_SIZING_IS_INIT() (SRCU_SIZING_IS(SRCU_SIZING_INIT)) +#define SRCU_SIZING_IS_TORTURE() (SRCU_SIZING_IS(SRCU_SIZING_TORTURE)) +#define SRCU_SIZING_IS_CONTEND() (convert_to_big & SRCU_SIZING_CONTEND) +static int convert_to_big = SRCU_SIZING_NONE; module_param(convert_to_big, int, 0444); +/* Contention events per jiffy to initiate transition to big. */ +static int small_contention_lim __read_mostly = 100; +module_param(small_contention_lim, int, 0444); + /* Early-boot callback-management, so early that no lock is required! */ static LIST_HEAD(srcu_boot_list); static bool __read_mostly srcu_init_done; @@ -58,31 +74,40 @@ static void process_srcu(struct work_struct *work); static void srcu_delay_timer(struct timer_list *t); /* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */ -#define spin_lock_rcu_node(p) \ -do { \ - spin_lock(&ACCESS_PRIVATE(p, lock)); \ - smp_mb__after_unlock_lock(); \ +#define spin_lock_rcu_node(p) \ +do { \ + spin_lock(&ACCESS_PRIVATE(p, lock)); \ + smp_mb__after_unlock_lock(); \ } while (0) #define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock)) -#define spin_lock_irq_rcu_node(p) \ -do { \ - spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \ - smp_mb__after_unlock_lock(); \ +#define spin_lock_irq_rcu_node(p) \ +do { \ + spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \ + smp_mb__after_unlock_lock(); \ } while (0) -#define spin_unlock_irq_rcu_node(p) \ +#define spin_unlock_irq_rcu_node(p) \ spin_unlock_irq(&ACCESS_PRIVATE(p, lock)) -#define spin_lock_irqsave_rcu_node(p, flags) \ -do { \ - spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ - smp_mb__after_unlock_lock(); \ +#define spin_lock_irqsave_rcu_node(p, flags) \ +do { \ + spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ + smp_mb__after_unlock_lock(); \ } while (0) -#define spin_unlock_irqrestore_rcu_node(p, flags) \ - spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \ +#define spin_trylock_irqsave_rcu_node(p, flags) \ +({ \ + bool ___locked = spin_trylock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ + \ + if (___locked) \ + smp_mb__after_unlock_lock(); \ + ___locked; \ +}) + +#define spin_unlock_irqrestore_rcu_node(p, flags) \ + spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \ /* * Initialize SRCU per-CPU data. Note that statically allocated @@ -225,7 +250,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) init_srcu_struct_data(ssp); ssp->srcu_gp_seq_needed_exp = 0; ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); - if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 1) { + if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) { if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC)) { if (!ssp->sda_is_static) { free_percpu(ssp->sda); @@ -273,6 +298,15 @@ EXPORT_SYMBOL_GPL(init_srcu_struct); #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ /* + * Initiate a transition to SRCU_SIZE_BIG with lock held. + */ +static void __srcu_transition_to_big(struct srcu_struct *ssp) +{ + lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock)); + smp_store_release(&ssp->srcu_size_state, SRCU_SIZE_ALLOC); +} + +/* * Initiate an idempotent transition to SRCU_SIZE_BIG. */ static void srcu_transition_to_big(struct srcu_struct *ssp) @@ -287,11 +321,36 @@ static void srcu_transition_to_big(struct srcu_struct *ssp) spin_unlock_irqrestore_rcu_node(ssp, flags); return; } - smp_store_release(&ssp->srcu_size_state, SRCU_SIZE_ALLOC); + __srcu_transition_to_big(ssp); spin_unlock_irqrestore_rcu_node(ssp, flags); } /* + * Acquire the specified srcu_struct structure's ->lock, but check for + * excessive contention, which results in initiation of a transition + * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module + * parameter permits this. + */ +static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned long *flags) +{ + unsigned long j; + + if (spin_trylock_irqsave_rcu_node(ssp, *flags)) + return; + spin_lock_irqsave_rcu_node(ssp, *flags); + if (!SRCU_SIZING_IS_CONTEND() || ssp->srcu_size_state) + return; + j = jiffies; + if (ssp->srcu_size_jiffies != j) { + ssp->srcu_size_jiffies = j; + ssp->srcu_n_lock_retries = 0; + } + if (++ssp->srcu_n_lock_retries <= small_contention_lim) + return; + __srcu_transition_to_big(ssp); +} + +/* * First-use initialization of statically allocated srcu_struct * structure. Wiring up the combining tree is more than can be * done with compile-time initialization, so this check is added @@ -718,7 +777,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); spin_unlock_irqrestore_rcu_node(snp, flags); } - spin_lock_irqsave_rcu_node(ssp, flags); + spin_lock_irqsave_ssp_contention(ssp, &flags); if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); spin_unlock_irqrestore_rcu_node(ssp, flags); @@ -779,7 +838,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, } /* Top of tree, must ensure the grace period will be started. */ - spin_lock_irqsave_rcu_node(ssp, flags); + spin_lock_irqsave_ssp_contention(ssp, &flags); if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed, s)) { /* * Record need for grace period s. Pair with load @@ -1542,7 +1601,7 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) } pr_cont(" T(%ld,%ld)\n", s0, s1); } - if (convert_to_big == 2) + if (SRCU_SIZING_IS_TORTURE()) srcu_transition_to_big(ssp); } EXPORT_SYMBOL_GPL(srcu_torture_stats_print); |