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sunrpc: guarantee a thread per pool when auto-distributing

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svc_set_num_threads() spreads the requested thread count evenly across
the service's pools. In pernode mode each pool maps to a NUMA node, and
svc_pool_for_cpu() steers an incoming transport to the pool for the node
it arrived on. When fewer threads than pools are requested, even
distribution leaves some pools empty, and a transport steered to an
empty pool has no thread to service it.

Floor each pool at one thread when auto-distributing a non-zero count,
so no pool is left empty. Every pool maps to a node that had CPUs when
the pool map was built (svc_pool_map_init_pernode() only creates pools
for nodes returned by for_each_node_with_cpus()), so there is no pool
that should be left threadless. The resulting total may exceed the
requested count. This only affects the auto-distribute path (a
single-value array, i.e. svc_set_num_threads()); callers that set
per-pool counts explicitly via svc_set_pool_threads() are unchanged and
may still set a pool to zero.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20260706-sunrpc-pool-mode-v5-3-6c4ee7cd89aa@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
This commit is contained in:
Jeff Layton
2026-07-06 09:29:23 -04:00
committed by Chuck Lever
parent a1a7071195
commit f59c4b77d6
1 changed files with 16 additions and 0 deletions
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16
net/sunrpc/svc.c
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@@ -837,6 +837,12 @@ EXPORT_SYMBOL_GPL(svc_set_pool_threads);
* are multiple pools then the new threads or victims will be distributed
* evenly among them.
*
* When @nrservs is non-zero but smaller than the number of pools, even
* distribution would leave some pools empty. Since each pool maps to a
* NUMA node and only services transports steered to that node, every
* pool is instead guaranteed at least one thread. The resulting total
* may therefore exceed @nrservs.
*
* Caller must ensure mutual exclusion between this and server startup or
* shutdown.
*
@@ -852,6 +858,16 @@ svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
unsigned int remain = nrservs % serv->sv_nrpools;
int i, err = 0;
/*
* Don't let a pool sit empty while threads are being
* auto-distributed: a transport steered to its node would have
* nothing to service it. Every pool maps to a CPU-bearing node,
* so hand each one a thread. This may push the total above
* @nrservs.
*/
if (base == 0 && nrservs != 0)
remain = serv->sv_nrpools;
for (i = 0; i < serv->sv_nrpools; ++i) {
struct svc_pool *pool = &serv->sv_pools[i];
int threads = base;