This commit adds an srcu_tree.convert_to_big kernel parameter that either
refuses to convert at all (0), converts immediately at init_srcu_struct()
time (1), or lets rcutorture convert it (2). An addition contention-based
dynamic conversion choice will be added, along with documentation.
[ paulmck: Apply callback-scanning feedback from Neeraj Upadhyay. ]
Co-developed-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
.../admin-guide/kernel-parameters.txt | 13 +++++
kernel/rcu/srcutree.c | 48 ++++++++++++-------
2 files changed, 45 insertions(+), 16 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3f1cc5e317ed..1f1fcac7777d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5608,6 +5608,19 @@
off: Disable mitigation and remove
performance impact to RDRAND and RDSEED
+ srcutree.convert_to_big [KNL]
+ Specifies under what conditions an SRCU tree
+ srcu_struct structure will be converted to big
+ form, that is, with an rcu_node tree:
+
+ 0: Never.
+ 1: At init_srcu_struct() time.
+ 2: When rcutorture decides to.
+
+ Either way, the srcu_node tree will be sized based
+ on the actual runtime number of CPUs (nr_cpu_ids)
+ instead of the compile-time CONFIG_NR_CPUS.
+
srcutree.counter_wrap_check [KNL]
Specifies how frequently to check for
grace-period sequence counter wrap for the
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 2e7ed67646db..9dd048989027 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -39,6 +39,15 @@ module_param(exp_holdoff, ulong, 0444);
static ulong counter_wrap_check = (ULONG_MAX >> 2);
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().
+ */
+static int convert_to_big;
+module_param(convert_to_big, 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;
@@ -123,7 +132,7 @@ static inline bool srcu_invl_snp_seq(unsigned long s)
* Allocated and initialize SRCU combining tree. Returns @true if
* allocation succeeded and @false otherwise.
*/
-static bool init_srcu_struct_nodes(struct srcu_struct *ssp)
+static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
{
int cpu;
int i;
@@ -135,7 +144,7 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp)
/* Initialize geometry if it has not already been initialized. */
rcu_init_geometry();
- ssp->node = kcalloc(rcu_num_nodes, sizeof(*ssp->node), GFP_ATOMIC);
+ ssp->node = kcalloc(rcu_num_nodes, sizeof(*ssp->node), gfp_flags);
if (!ssp->node)
return false;
@@ -213,17 +222,19 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
if (!ssp->sda)
return -ENOMEM;
init_srcu_struct_data(ssp);
- if (!init_srcu_struct_nodes(ssp)) {
- if (!is_static) {
- free_percpu(ssp->sda);
- ssp->sda = NULL;
- return -ENOMEM;
- }
- } else {
- ssp->srcu_size_state = SRCU_SIZE_BIG;
- }
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 (!init_srcu_struct_nodes(ssp, GFP_ATOMIC)) {
+ if (!is_static) {
+ free_percpu(ssp->sda);
+ ssp->sda = NULL;
+ return -ENOMEM;
+ }
+ } else {
+ WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_BIG);
+ }
+ }
smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */
return 0;
}
@@ -594,7 +605,8 @@ static void srcu_gp_end(struct srcu_struct *ssp)
/* A new grace period can start at this point. But only one. */
/* Initiate callback invocation as needed. */
- if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER) {
+ ss_state = smp_load_acquire(&ssp->srcu_size_state);
+ if (ss_state < SRCU_SIZE_WAIT_BARRIER) {
srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, 0), cbdelay);
} else {
idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
@@ -603,13 +615,16 @@ static void srcu_gp_end(struct srcu_struct *ssp)
cbs = false;
last_lvl = snp >= ssp->level[rcu_num_lvls - 1];
if (last_lvl)
- cbs = snp->srcu_have_cbs[idx] == gpseq;
+ cbs = ss_state < SRCU_SIZE_BIG || snp->srcu_have_cbs[idx] == gpseq;
snp->srcu_have_cbs[idx] = gpseq;
rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
sgsne = snp->srcu_gp_seq_needed_exp;
if (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, gpseq))
WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
- mask = snp->srcu_data_have_cbs[idx];
+ if (ss_state < SRCU_SIZE_BIG)
+ mask = ~0;
+ else
+ mask = snp->srcu_data_have_cbs[idx];
snp->srcu_data_have_cbs[idx] = 0;
spin_unlock_irq_rcu_node(snp);
if (cbs)
@@ -645,10 +660,9 @@ static void srcu_gp_end(struct srcu_struct *ssp)
}
/* Transition to big if needed. */
- ss_state = smp_load_acquire(&ssp->srcu_size_state);
if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
if (ss_state == SRCU_SIZE_ALLOC)
- init_srcu_struct_nodes(ssp);
+ init_srcu_struct_nodes(ssp, GFP_KERNEL);
else
smp_store_release(&ssp->srcu_size_state, ss_state + 1);
}
@@ -1494,6 +1508,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
s1 += c1;
}
pr_cont(" T(%ld,%ld)\n", s0, s1);
+ if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 2)
+ WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_ALLOC);
}
EXPORT_SYMBOL_GPL(srcu_torture_stats_print);
--
2.31.1.189.g2e36527f23
