[PATCH v5 5/5] sunrpc: derive the pool count instead of caching it in sv_nrpools
From: Jeff Layton
Date: Mon Jul 06 2026 - 11:18:47 EST
Now that the pool mode is always pernode, svc_serv.sv_nrpools is
redundant with sv_is_pooled: an unpooled service always has a single
pool, and a pooled service has svc_pool_map.npools pools (which is one on
a single-node host). sv_nrpools cannot distinguish an unpooled service
from a pooled service that happens to have one pool, so it is sv_nrpools,
not sv_is_pooled, that carries no unique information.
Replace the cached field with a svc_serv_nrpools() helper that derives
the count from sv_is_pooled and the pool map, and convert all readers to
it. svc_pool_map is file-local to svc.c, so export the helper for the
svc_xprt.c and nfsd callers.
Reading svc_pool_map.npools without svc_pool_map_mutex is safe: the
mutex protects only svc_pool_map.count, and npools is already read
locklessly in svc_pool_for_cpu().
A pooled service holds a map reference for its whole lifetime, so npools
is stable while any reader could observe it. The hot path
(svc_pool_for_cpu()) already dereferences svc_pool_map for to_pool, and
npools shares that cacheline, so there is no new locking or coherence
cost.
__svc_create() keeps using its local npools argument for the sv_pools[]
allocation, since sv_is_pooled is not set until svc_create_pooled() has
returned from it.
Doing this also removes a modulus operation from svc_pool_for_cpu(),
which should make for more efficient RPC queueing.
Assisted-by: Claude:claude-opus-4-8
Suggested-by: NeilBrown <neilb@xxxxxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
fs/nfsd/nfsctl.c | 2 +-
fs/nfsd/nfssvc.c | 10 ++++-----
include/linux/sunrpc/svc.h | 2 +-
net/sunrpc/svc.c | 52 ++++++++++++++++++++++++++++++++--------------
net/sunrpc/svc_xprt.c | 6 +++---
5 files changed, 46 insertions(+), 26 deletions(-)
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index bc16fc7ca24f..0543e5bb842f 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1526,7 +1526,7 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
rcu_read_lock();
- for (i = 0; i < nn->nfsd_serv->sv_nrpools; i++) {
+ for (i = 0; i < svc_serv_nrpools(nn->nfsd_serv); i++) {
struct svc_rqst *rqstp;
long thread_skip = 0;
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index a8ea4dbfa56b..2edf716ea022 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -655,7 +655,7 @@ int nfsd_nrpools(struct net *net)
if (nn->nfsd_serv == NULL)
return 0;
else
- return nn->nfsd_serv->sv_nrpools;
+ return svc_serv_nrpools(nn->nfsd_serv);
}
int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
@@ -665,7 +665,7 @@ int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
int i;
if (serv)
- for (i = 0; i < serv->sv_nrpools && i < n; i++)
+ for (i = 0; i < svc_serv_nrpools(serv) && i < n; i++)
nthreads[i] = serv->sv_pools[i].sp_nrthrmax;
return 0;
}
@@ -699,8 +699,8 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
if (n == 1)
return svc_set_num_threads(nn->nfsd_serv, nn->min_threads, nthreads[0]);
- if (n > nn->nfsd_serv->sv_nrpools)
- n = nn->nfsd_serv->sv_nrpools;
+ if (n > svc_serv_nrpools(nn->nfsd_serv))
+ n = svc_serv_nrpools(nn->nfsd_serv);
/* enforce a global maximum number of threads */
tot = 0;
@@ -731,7 +731,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
}
/* Anything undefined in array is considered to be 0 */
- for (i = n; i < nn->nfsd_serv->sv_nrpools; ++i) {
+ for (i = n; i < svc_serv_nrpools(nn->nfsd_serv); ++i) {
err = svc_set_pool_threads(nn->nfsd_serv,
&nn->nfsd_serv->sv_pools[i],
0, 0);
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 3a0152d926fb..3c885ab6ad41 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -85,7 +85,6 @@ struct svc_serv {
char * sv_name; /* service name */
- unsigned int sv_nrpools; /* number of thread pools */
bool sv_is_pooled; /* is this a pooled service? */
struct svc_pool * sv_pools; /* array of thread pools */
int (*sv_threadfn)(void *data);
@@ -480,6 +479,7 @@ void svc_wake_up(struct svc_serv *);
void svc_reserve(struct svc_rqst *rqstp, int space);
void svc_pool_wake_idle_thread(struct svc_pool *pool);
struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv);
+unsigned int svc_serv_nrpools(const struct svc_serv *serv);
char * svc_print_addr(struct svc_rqst *, char *, size_t);
const char * svc_proc_name(const struct svc_rqst *rqstp);
int svc_encode_result_payload(struct svc_rqst *rqstp,
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index ece69cb0138a..800514a14f17 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -224,7 +224,7 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
unsigned int node = m->pool_to[pidx];
/*
- * The caller checks for sv_nrpools > 1, which
+ * The caller checks for more than one pool, which
* implies that we've been initialized.
*/
WARN_ON_ONCE(m->count == 0);
@@ -234,6 +234,24 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
set_cpus_allowed_ptr(task, cpumask_of_node(node));
}
+/**
+ * svc_serv_nrpools - number of thread pools backing a service
+ * @serv: An RPC service
+ *
+ * Pooled services all share the global svc_pool_map, so their pool count
+ * is svc_pool_map.npools. Unpooled services have a single pool. Reading
+ * npools without svc_pool_map_mutex is safe: a pooled service holds a map
+ * reference for its whole lifetime, so npools is stable once set.
+ *
+ * Return value:
+ * The number of pools in @serv
+ */
+unsigned int svc_serv_nrpools(const struct svc_serv *serv)
+{
+ return serv->sv_is_pooled ? svc_pool_map.npools : 1;
+}
+EXPORT_SYMBOL_GPL(svc_serv_nrpools);
+
/**
* svc_pool_for_cpu - Select pool to run a thread on this cpu
* @serv: An RPC service
@@ -247,12 +265,15 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
{
struct svc_pool_map *m = &svc_pool_map;
+ unsigned int nrpools = svc_serv_nrpools(serv);
unsigned int pidx, i;
- if (serv->sv_nrpools <= 1)
+ if (nrpools <= 1)
return serv->sv_pools;
- pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())] % serv->sv_nrpools;
+ pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())];
+ if (pidx >= nrpools)
+ pidx = 0;
/*
* It's possible to have a pool with no threads. Userland can just set
@@ -265,7 +286,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
* populated pool, trading NUMA locality for a guarantee that the
* transport is serviced.
*/
- for (i = 0; i < serv->sv_nrpools; i++) {
+ for (i = 0; i < nrpools; i++) {
struct svc_pool *pool = &serv->sv_pools[pidx];
/* This is set under the sp_mutex and rarely ever changes. A
@@ -274,7 +295,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
if (data_race(pool->sp_nrthreads))
return pool;
- if (++pidx >= serv->sv_nrpools)
+ if (++pidx >= nrpools)
pidx = 0;
}
@@ -414,15 +435,13 @@ __svc_create(struct svc_program *prog, int nprogs, struct svc_stat *stats,
__svc_init_bc(serv);
- serv->sv_nrpools = npools;
- serv->sv_pools =
- kzalloc_objs(struct svc_pool, serv->sv_nrpools);
+ serv->sv_pools = kzalloc_objs(struct svc_pool, npools);
if (!serv->sv_pools) {
kfree(serv);
return NULL;
}
- for (i = 0; i < serv->sv_nrpools; i++) {
+ for (i = 0; i < npools; i++) {
struct svc_pool *pool = &serv->sv_pools[i];
dprintk("svc: initialising pool %u for %s\n",
@@ -520,7 +539,7 @@ svc_destroy(struct svc_serv **servp)
cache_clean_deferred(serv);
- for (i = 0; i < serv->sv_nrpools; i++) {
+ for (i = 0; i < svc_serv_nrpools(serv); i++) {
struct svc_pool *pool = &serv->sv_pools[i];
svc_pool_destroy_counters(pool);
@@ -732,7 +751,7 @@ int svc_new_thread(struct svc_serv *serv, struct svc_pool *pool)
}
rqstp->rq_task = task;
- if (serv->sv_nrpools > 1)
+ if (svc_serv_nrpools(serv) > 1)
svc_pool_map_set_cpumask(task, pool->sp_id);
svc_sock_update_bufs(serv);
@@ -858,8 +877,9 @@ int
svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
unsigned int nrservs)
{
- unsigned int base = nrservs / serv->sv_nrpools;
- unsigned int remain = nrservs % serv->sv_nrpools;
+ unsigned int nrpools = svc_serv_nrpools(serv);
+ unsigned int base = nrservs / nrpools;
+ unsigned int remain = nrservs % nrpools;
int i, err = 0;
/*
@@ -870,9 +890,9 @@ svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
* @nrservs.
*/
if (base == 0 && nrservs != 0)
- remain = serv->sv_nrpools;
+ remain = nrpools;
- for (i = 0; i < serv->sv_nrpools; ++i) {
+ for (i = 0; i < nrpools; ++i) {
struct svc_pool *pool = &serv->sv_pools[i];
int threads = base;
@@ -906,7 +926,7 @@ unsigned int svc_serv_maxthreads(const struct svc_serv *serv)
{
unsigned int i, max = 0;
- for (i = 0; i < serv->sv_nrpools; i++)
+ for (i = 0; i < svc_serv_nrpools(serv); i++)
max += data_race(serv->sv_pools[i].sp_nrthrmax);
return max;
}
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 63d1002e63e7..40040af588fb 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1188,7 +1188,7 @@ static void svc_clean_up_xprts(struct svc_serv *serv, struct net *net)
struct svc_xprt *xprt;
int i;
- for (i = 0; i < serv->sv_nrpools; i++) {
+ for (i = 0; i < svc_serv_nrpools(serv); i++) {
struct svc_pool *pool = &serv->sv_pools[i];
struct llist_node *q, **t1, *t2;
@@ -1517,7 +1517,7 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
return SEQ_START_TOKEN;
if (!si->serv)
return NULL;
- return pidx > si->serv->sv_nrpools ? NULL
+ return pidx > svc_serv_nrpools(si->serv) ? NULL
: &si->serv->sv_pools[pidx - 1];
}
@@ -1535,7 +1535,7 @@ static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
pool = &serv->sv_pools[0];
} else {
unsigned int pidx = (pool - &serv->sv_pools[0]);
- if (pidx < serv->sv_nrpools-1)
+ if (pidx < svc_serv_nrpools(serv) - 1)
pool = &serv->sv_pools[pidx+1];
else
pool = NULL;
--
2.55.0