Re: [PATCH v3 0/4] Reduce lock contention in the NFS client

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2026-09-15 at 10:20 -0400, Chuck Lever wrote:
> Under a 4KB NFSv3 workload on 100GbE RDMA, roughly 150 RPC worker
> threads drive the client, and lock contention dominates its CPU
> profile: up to 53% of non-idle cycles are spent in
> native_queued_spin_lock_slowpath.
> 
> Three locks account for that: reserve_lock on every XID
> allocation, queue_lock on every submit and completion, and the
> unbound worker pool lock on every enqueue and dequeue for rpciod,
> nfsiod, and xprtiod.
> 
> This series addresses the first two. v2 also moved the three
> workqueues to the WQ_AFFN_SMT scope. Tim Menninger reported an
> intermittent throughput regression on a 96-CPU two-socket
> NFS/RDMA client and bisected it to the rpciod scope change [1].
> The cause is still being worked out in that thread, so the scope
> patches are withdrawn until it is understood. Until then, WQ_SYSFS
> on all three workqueues lets an administrator set the scope from
> user space.
> 
> [1] https://lore.kernel.org/linux-nfs/20260902204048.4100864-1-tmenninger@everpuredata.com/
> 
> ---
> Changes in v3:
> - Drop the WQ_AFFN_SMT scope patches (Tim Menninger's regression report)
> - Rebase on v7.3-rc2
> - Link to v2: https://patch.msgid.link/20260902-performance-v2-0-b71c0c082f9d@kernel.org
> 
> Changes in v2:
> - Fix send bvec use-after-free in xprt_request_dequeue_xprt() (sashiko)
> - Replace the three workqueue exports with workqueue_set_affn_scope()
> - Split the WQ_SYSFS patch into SUNRPC and NFS patches
> - Drop v1 patch 2: async completions in the submitter can deadlock
> - Correct the pool cost and SMT group wording in the scope patches
> - Link to v1: https://patch.msgid.link/20260831-performance-v1-0-8d9fd9b67f96@kernel.org
> 
> ---
> Chuck Lever (4):
>       SUNRPC: Use atomic_t for XID allocation
>       SUNRPC: Split recv_lock out of xprt->queue_lock
>       SUNRPC: Set WQ_SYSFS on rpciod and xprtiod
>       NFS: Set WQ_SYSFS on nfsiod
> 
>  fs/nfs/inode.c                             |  3 +-
>  include/linux/sunrpc/xprt.h                |  8 ++-
>  net/sunrpc/sched.c                         |  5 +-
>  net/sunrpc/svcsock.c                       |  6 +--
>  net/sunrpc/xprt.c                          | 85 ++++++++++++++++++------------
>  net/sunrpc/xprtrdma/rpc_rdma.c             | 14 ++---
>  net/sunrpc/xprtrdma/svc_rdma_backchannel.c |  8 +--
>  net/sunrpc/xprtsock.c                      | 18 +++----
>  8 files changed, 85 insertions(+), 62 deletions(-)
> ---
> base-commit: df2908090cda368b01ff43709f51890076c56157
> change-id: 20260831-performance-e465e621c1c0
> 
> Best regards,
> --  
> Chuck Lever

Nice, straightforward performance wins!

Reviewed-by: Jeff Layton <jlayton@kernel.org>