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srcu: Add boot-time control over srcu_node array allocation

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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@quicinc.com>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-01-25 15:41:10 -08:00
parent 0b56f95390
commit c69a00a12e
2 changed files with 45 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

48
kernel/rcu/srcutree.c
View File

@ -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);