From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A937F390229; Wed, 8 Jul 2026 23:37:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783553861; cv=none; b=X7WdL3jvgaip+TBe4Rkg1wh1Gf2yYIuTQQVzxNwU6ok5KCtkMmXdNTxgNMB3p/WqBwuHMQOquM0SmO0LWs9UNevAzXx5TmU2LXsoUBrmSz102I6xA2H7vQgtNIofHm4H97zIZIaHsyc6SdSYIQ0JVV+BHdx3F2Qqb8Vys+vjFlE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783553861; c=relaxed/simple; bh=dxUAcrFUmm+bZtduqwrowE/jGK6Gh4L8LiIQl8gDsSE=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=PGUC2pejIjzA4eUsf9Lmgb7VwJ+h5q57aT6TRs9Mgo1wsb/rBvHiZQ7peFJoS7WgzqJzL/zz+g6oaAPm0ndLvN8X/ZGgtmXS0OYlESsjuzU+2ts8xqx888BpYLslBBWpTk0/mySKnWfJhIWspln1V14RV1z573Fb710ivUet0hg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h+DBeNe0; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="h+DBeNe0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7563D1F000E9; Wed, 8 Jul 2026 23:37:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783553859; bh=godA7roKAFqIy4dp2iHpnLhUNgnPzXUBnLo+/sDTGlY=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=h+DBeNe0vtIGG4NKiDXD/ND0vImHvXKNZPxj1F/Cfx1g6aoKAlD/ioOR+WwSygxVr JYtDlw3Snx7MDFaRbEUbUVrhkQxaQ/zggH3C7XIU+NfeMELpYTqRolCrry2VLzHd7j CZYb8YgqqWWJztVBvhbVv3gjvGRuaxs1u0i/axrblJr0gSr4lJ2q1pJ93doPUZHY3o EaRvf5xjXyoJf5ah4O1CEulXU5LzRX9wcW9PqRLES7NG+N/kBiXZMVTJEMa5qovirT LE9KmLUNCUNT5sK977UabpfJugLAo9YK1ex5tqEEr37dwEO8q8B7zKVECv8scBNnjt QLYMIttvu2dpA== Message-ID: <44491689bfb3340f618829da785a302594f476f4.camel@kernel.org> Subject: Re: [PATCH v5 5/5] sunrpc: derive the pool count instead of caching it in sv_nrpools From: Jeff Layton To: NeilBrown Cc: Trond Myklebust , Anna Schumaker , Olga Kornievskaia , Dai Ngo , Tom Talpey , Chuck Lever , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 08 Jul 2026 19:37:37 -0400 In-Reply-To: <178355109748.3371781.17923928016828009638@noble.neil.brown.name> References: <20260706-sunrpc-pool-mode-v5-0-6c4ee7cd89aa@kernel.org> <20260706-sunrpc-pool-mode-v5-5-6c4ee7cd89aa@kernel.org> <178337823128.27465.5531515481696438438@noble.neil.brown.name> <3496ed08e534a3e81dfe4168d4b2bc3c325d829a.camel@kernel.org> <178348882124.3371781.3092732814258907420@noble.neil.brown.name> <6f703524141a195ad1e4f16b1b1d16ffa2073189.camel@kernel.org> 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f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2026-07-09 at 08:51 +1000, NeilBrown wrote: > On Wed, 08 Jul 2026, Jeff Layton wrote: > > On Wed, 2026-07-08 at 15:33 +1000, NeilBrown wrote: > > > On Tue, 07 Jul 2026, Jeff Layton wrote: > > > > On Tue, 2026-07-07 at 08:50 +1000, NeilBrown wrote: > > > > > On Mon, 06 Jul 2026, Jeff Layton wrote: > > > > > > Now that the pool mode is always pernode, svc_serv.sv_nrpools i= s > > > > > > redundant with sv_is_pooled: an unpooled service always has a s= ingle > > > > > > 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 s= v_nrpools, > > > > > > not sv_is_pooled, that carries no unique information. > > > > > >=20 > > > > > > 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 r= eaders to > > > > > > it. svc_pool_map is file-local to svc.c, so export the helper f= or the > > > > > > svc_xprt.c and nfsd callers. > > > > > >=20 > > > > > > Reading svc_pool_map.npools without svc_pool_map_mutex is safe:= the > > > > > > mutex protects only svc_pool_map.count, and npools is already r= ead > > > > > > locklessly in svc_pool_for_cpu(). > > > > > >=20 > > > > > > 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_p= ool, and > > > > > > npools shares that cacheline, so there is no new locking or coh= erence > > > > > > cost. > > > > > >=20 > > > > > > __svc_create() keeps using its local npools argument for the sv= _pools[] > > > > > > allocation, since sv_is_pooled is not set until svc_create_pool= ed() has > > > > > > returned from it. > > > > > >=20 > > > > > > Doing this also removes a modulus operation from svc_pool_for_c= pu(), > > > > > > which should make for more efficient RPC queueing. > > > > > >=20 > > > > > > Assisted-by: Claude:claude-opus-4-8 > > > > > > Suggested-by: NeilBrown > > > > > > Signed-off-by: Jeff Layton > > > > > > --- > > > > > > 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(-) > > > > > >=20 > > > > > > 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, > > > > > > =20 > > > > > > rcu_read_lock(); > > > > > > =20 > > > > > > - for (i =3D 0; i < nn->nfsd_serv->sv_nrpools; i++) { > > > > > > + for (i =3D 0; i < svc_serv_nrpools(nn->nfsd_serv); i++) { > > > > > > struct svc_rqst *rqstp; > > > > > > long thread_skip =3D 0; > > > > > > =20 > > > > > > 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 =3D=3D NULL) > > > > > > return 0; > > > > > > else > > > > > > - return nn->nfsd_serv->sv_nrpools; > > > > > > + return svc_serv_nrpools(nn->nfsd_serv); > > > > > > } > > > > > > =20 > > > > > > 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; > > > > > > =20 > > > > > > if (serv) > > > > > > - for (i =3D 0; i < serv->sv_nrpools && i < n; i++) > > > > > > + for (i =3D 0; i < svc_serv_nrpools(serv) && i < n; i++) > > > > > > nthreads[i] =3D 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 =3D=3D 1) > > > > > > return svc_set_num_threads(nn->nfsd_serv, nn->min_threads, n= threads[0]); > > > > > > =20 > > > > > > - if (n > nn->nfsd_serv->sv_nrpools) > > > > > > - n =3D nn->nfsd_serv->sv_nrpools; > > > > > > + if (n > svc_serv_nrpools(nn->nfsd_serv)) > > > > > > + n =3D svc_serv_nrpools(nn->nfsd_serv); > > > > > > =20 > > > > > > /* enforce a global maximum number of threads */ > > > > > > tot =3D 0; > > > > > > @@ -731,7 +731,7 @@ int nfsd_set_nrthreads(int n, int *nthreads= , struct net *net) > > > > > > } > > > > > > =20 > > > > > > /* Anything undefined in array is considered to be 0 */ > > > > > > - for (i =3D n; i < nn->nfsd_serv->sv_nrpools; ++i) { > > > > > > + for (i =3D n; i < svc_serv_nrpools(nn->nfsd_serv); ++i) { > > > > > > err =3D 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 { > > > > > > =20 > > > > > > char * sv_name; /* service name */ > > > > > > =20 > > > > > > - 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 =3D m->pool_to[pidx]; > > > > > > =20 > > > > > > /* > > > > > > - * 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 =3D=3D 0); > > > > > > @@ -234,6 +234,24 @@ svc_pool_map_set_cpumask(struct task_struc= t *task, unsigned int pidx) > > > > > > set_cpus_allowed_ptr(task, cpumask_of_node(node)); > > > > > > } > > > > > > =20 > > > > > > +/** > > > > > > + * 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 poo= l. 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); > > > > >=20 > > > > > I would make this a static-inline. > > > > >=20 > > > >=20 > > > > That would mean that we would have to export svc_pool_map, which is > > > > currently private to svc.c. > > >=20 > > > Why is exporting svc_pool_map more problematic than exporting svc_ser= v_nrpools? > > > I think it would be good for at least the code in svc_pool_for_cpu() = to > > > inline the function. Maybe it already does? Or maybe marking it > > > "inline" but still exporting it would work. > > >=20 > > > Thanks, > > > NeilBrown > > >=20 > >=20 > > Doing what you suggest would increase the interface "surface" between > > sunrpc.ko and nfsd.ko. > >=20 > > Currently struct svc_pool_map is only defined in net/sunrpc/svc.c, so > > we'd not only need to export the symbol, but also we'd have to make > > that definition public. > >=20 > > Why expose so many internal details to other modules when all we need > > is this one accessor? I think keeping this interface small is > > preferable. >=20 > In general, yes. But it is not without cost. Sometimes the cost > matters. > Interface size has an abstract value. Code size can have concrete > value. Comparing them is subjective I guess. > I have no concrete evidence that there is a problem, so I'll stop > objecting. >=20 Your point is certainly valid, and this _is_ a hot path. If we can demonstrate that this matters, then I'd be happy to revisit the idea. I don't have the cycles to do so at the moment though. --=20 Jeff Layton