sunrpc: route to a populated pool in svc_pool_for_cpu()

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svc_set_num_threads() spreads the requested threads evenly across the
service's pools (base = nrservs / sv_nrpools).  When a service runs
fewer threads than it has pools -- e.g. an nfsd configured with fewer
threads than the host has NUMA nodes while running in "pernode" or
"percpu" mode -- the trailing pools are left with no threads at all.

svc_xprt_enqueue() selects a pool from the CPU servicing the transport,
queues the transport on that pool's sp_xprts, and only wakes a thread
from the same pool.  Each thread services exclusively its own pool, so a
transport that lands on a threadless pool is enqueued on sp_xprts and
never picked up: the connection hangs indefinitely.

Have svc_pool_for_cpu() skip pools that currently have no threads,
falling back to the next populated pool.  This trades NUMA locality for
a guarantee that the work is actually serviced.  sp_nrthreads is only
updated under the service mutex; the lockless read here is a best-effort
routing hint, so annotate it with data_race().

Fixes: bfd241600a ("[PATCH] knfsd: make rpc threads pools numa aware")
Cc: stable@vger.kernel.org
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260706-sunrpc-pool-mode-v5-1-6c4ee7cd89aa@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

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Jeff Layton 2026-07-06 09:29:21 -04:00 • committed by Chuck Lever

parent 0574da29ae

commit f6310491c4

1 changed files with 28 additions and 1 deletions

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net/sunrpc/svc.c

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