[PATCH net-next v3 1/2] net/smc: make wr buffer count configurable

Halil Pasic
2025-09-21T21:45:03Z

Think SMC_WR_BUF_CNT_SEND := SMC_WR_BUF_CNT used in send context and
SMC_WR_BUF_CNT_RECV := 3 * SMC_WR_BUF_CNT used in recv context. Those
get replaced with lgr->max_send_wr and lgr->max_recv_wr respective.

While at it let us also remove a confusing comment that is either not
about the context in which it resides (describing
qp_attr.cap.max_send_wr and qp_attr.cap.max_recv_wr) or not applicable
any more when these values become configurable.

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
---
Documentation/networking/smc-sysctl.rst | 36 +++++++++++++++++++++++++
include/net/netns/smc.h | 2 ++
net/smc/smc_core.h | 6 +++++
net/smc/smc_ib.c | 7 ++---
net/smc/smc_llc.c | 2 ++
net/smc/smc_sysctl.c | 22 +++++++++++++++
net/smc/smc_sysctl.h | 2 ++
net/smc/smc_wr.c | 32 +++++++++++-----------
net/smc/smc_wr.h | 2 --
9 files changed, 89 insertions(+), 22 deletions(-)

diff --git a/Documentation/networking/smc-sysctl.rst b/Documentation/networking/smc-sysctl.rst
index a874d007f2db..c94d750c7c84 100644
--- a/Documentation/networking/smc-sysctl.rst
+++ b/Documentation/networking/smc-sysctl.rst
@@ -71,3 +71,39 @@ smcr_max_conns_per_lgr - INTEGER
acceptable value ranges from 16 to 255. Only for SMC-R v2.1 and later.

Default: 255
+
+smcr_max_send_wr - INTEGER
+ So called work request buffers are SMCR link (and RDMA queue pair) level
+ resources necessary for performing RDMA operations. Since up to 255
+ connections can share a link group and thus also a link and the number
+ of the work request buffers is decided when the link is allocated,
+ depending on the workload it can a bottleneck in a sense that threads
+ have to wait for work request buffers to become available. Before the
+ introduction of this control the maximal number of work request buffers
+ available on the send path used to be hard coded to 16. With this control
+ it becomes configurable. The acceptable range is between 2 and 2048.
+
+ Please be aware that all the buffers need to be allocated as a physically
+ continuous array in which each element is a single buffer and has the size
+ of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails we give up much
+ like before having this control.
+
+ Default: 16
+
+smcr_max_recv_wr - INTEGER
+ So called work request buffers are SMCR link (and RDMA queue pair) level
+ resources necessary for performing RDMA operations. Since up to 255
+ connections can share a link group and thus also a link and the number
+ of the work request buffers is decided when the link is allocated,
+ depending on the workload it can a bottleneck in a sense that threads
+ have to wait for work request buffers to become available. Before the
+ introduction of this control the maximal number of work request buffers
+ available on the receive path used to be hard coded to 16. With this control
+ it becomes configurable. The acceptable range is between 2 and 2048.
+
+ Please be aware that all the buffers need to be allocated as a physically
+ continuous array in which each element is a single buffer and has the size
+ of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails we give up much
+ like before having this control.
+
+ Default: 48
diff --git a/include/net/netns/smc.h b/include/net/netns/smc.h
index fc752a50f91b..6ceb12baec24 100644
--- a/include/net/netns/smc.h
+++ b/include/net/netns/smc.h
@@ -24,5 +24,7 @@ struct netns_smc {
int sysctl_rmem;
int sysctl_max_links_per_lgr;
int sysctl_max_conns_per_lgr;
+ unsigned int sysctl_smcr_max_send_wr;
+ unsigned int sysctl_smcr_max_recv_wr;
};
#endif
diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
index 48a1b1dcb576..ab2d15929cb2 100644
--- a/net/smc/smc_core.h
+++ b/net/smc/smc_core.h
@@ -33,6 +33,8 @@
* distributions may modify it to a value between
* 16-255 as needed.
*/
+#define SMCR_MAX_SEND_WR_DEF 16 /* Default number of work requests per send queue */
+#define SMCR_MAX_RECV_WR_DEF 48 /* Default number of work requests per recv queue */

struct smc_lgr_list { /* list of link group definition */
struct list_head list;
@@ -361,6 +363,10 @@ struct smc_link_group {
/* max conn can be assigned to lgr */
u8 max_links;
/* max links can be added in lgr */
+ u16 max_send_wr;
+ /* number of WR buffers on send */
+ u16 max_recv_wr;
+ /* number of WR buffers on recv */
};
struct { /* SMC-D */
struct smcd_gid peer_gid;
diff --git a/net/smc/smc_ib.c b/net/smc/smc_ib.c
index 0052f02756eb..e8d35c22c525 100644
--- a/net/smc/smc_ib.c
+++ b/net/smc/smc_ib.c
@@ -669,11 +669,6 @@ int smc_ib_create_queue_pair(struct smc_link *lnk)
.recv_cq = lnk->smcibdev->roce_cq_recv,
.srq = NULL,
.cap = {
- /* include unsolicited rdma_writes as well,
- * there are max. 2 RDMA_WRITE per 1 WR_SEND
- */
- .max_send_wr = SMC_WR_BUF_CNT * 3,
- .max_recv_wr = SMC_WR_BUF_CNT * 3,
.max_send_sge = SMC_IB_MAX_SEND_SGE,
.max_recv_sge = lnk->wr_rx_sge_cnt,
.max_inline_data = 0,
@@ -683,6 +678,8 @@ int smc_ib_create_queue_pair(struct smc_link *lnk)
};
int rc;

+ qp_attr.cap.max_send_wr = 3 * lnk->lgr->max_send_wr;
+ qp_attr.cap.max_recv_wr = lnk->lgr->max_recv_wr;
lnk->roce_qp = ib_create_qp(lnk->roce_pd, &qp_attr);
rc = PTR_ERR_OR_ZERO(lnk->roce_qp);
if (IS_ERR(lnk->roce_qp))
diff --git a/net/smc/smc_llc.c b/net/smc/smc_llc.c
index f865c58c3aa7..f5d5eb617526 100644
--- a/net/smc/smc_llc.c
+++ b/net/smc/smc_llc.c
@@ -2157,6 +2157,8 @@ void smc_llc_lgr_init(struct smc_link_group *lgr, struct smc_sock *smc)
init_waitqueue_head(&lgr->llc_msg_waiter);
init_rwsem(&lgr->llc_conf_mutex);
lgr->llc_testlink_time = READ_ONCE(net->smc.sysctl_smcr_testlink_time);
+ lgr->max_send_wr = (u16)(READ_ONCE(net->smc.sysctl_smcr_max_send_wr));
+ lgr->max_recv_wr = (u16)(READ_ONCE(net->smc.sysctl_smcr_max_recv_wr));
}

/* called after lgr was removed from lgr_list */
diff --git a/net/smc/smc_sysctl.c b/net/smc/smc_sysctl.c
index 2fab6456f765..7b2471904d04 100644
--- a/net/smc/smc_sysctl.c
+++ b/net/smc/smc_sysctl.c
@@ -29,6 +29,8 @@ static int links_per_lgr_min = SMC_LINKS_ADD_LNK_MIN;
static int links_per_lgr_max = SMC_LINKS_ADD_LNK_MAX;
static int conns_per_lgr_min = SMC_CONN_PER_LGR_MIN;
static int conns_per_lgr_max = SMC_CONN_PER_LGR_MAX;
+static unsigned int smcr_max_wr_min = 2;
+static unsigned int smcr_max_wr_max = 2048;

static struct ctl_table smc_table[] = {
{
@@ -99,6 +101,24 @@ static struct ctl_table smc_table[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
+ {
+ .procname = "smcr_max_send_wr",
+ .data = &init_net.smc.sysctl_smcr_max_send_wr,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &smcr_max_wr_min,
+ .extra2 = &smcr_max_wr_max,
+ },
+ {
+ .procname = "smcr_max_recv_wr",
+ .data = &init_net.smc.sysctl_smcr_max_recv_wr,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &smcr_max_wr_min,
+ .extra2 = &smcr_max_wr_max,
+ },
};

int __net_init smc_sysctl_net_init(struct net *net)
@@ -130,6 +150,8 @@ int __net_init smc_sysctl_net_init(struct net *net)
WRITE_ONCE(net->smc.sysctl_rmem, net_smc_rmem_init);
net->smc.sysctl_max_links_per_lgr = SMC_LINKS_PER_LGR_MAX_PREFER;
net->smc.sysctl_max_conns_per_lgr = SMC_CONN_PER_LGR_PREFER;
+ net->smc.sysctl_smcr_max_send_wr = SMCR_MAX_SEND_WR_DEF;
+ net->smc.sysctl_smcr_max_recv_wr = SMCR_MAX_RECV_WR_DEF;
/* disable handshake limitation by default */
net->smc.limit_smc_hs = 0;

diff --git a/net/smc/smc_sysctl.h b/net/smc/smc_sysctl.h
index eb2465ae1e15..8538915af7af 100644
--- a/net/smc/smc_sysctl.h
+++ b/net/smc/smc_sysctl.h
@@ -25,6 +25,8 @@ static inline int smc_sysctl_net_init(struct net *net)
net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
net->smc.sysctl_max_links_per_lgr = SMC_LINKS_PER_LGR_MAX_PREFER;
net->smc.sysctl_max_conns_per_lgr = SMC_CONN_PER_LGR_PREFER;
+ net->smc.sysctl_smcr_max_send_wr = SMCR_MAX_SEND_WR_DEF;
+ net->smc.sysctl_smcr_max_recv_wr = SMCR_MAX_RECV_WR_DEF;
return 0;
}

diff --git a/net/smc/smc_wr.c b/net/smc/smc_wr.c
index b04a21b8c511..f5b2772414fd 100644
--- a/net/smc/smc_wr.c
+++ b/net/smc/smc_wr.c
@@ -34,6 +34,7 @@
#define SMC_WR_MAX_POLL_CQE 10 /* max. # of compl. queue elements in 1 poll */

#define SMC_WR_RX_HASH_BITS 4
+
static DEFINE_HASHTABLE(smc_wr_rx_hash, SMC_WR_RX_HASH_BITS);
static DEFINE_SPINLOCK(smc_wr_rx_hash_lock);

@@ -547,9 +548,9 @@ void smc_wr_remember_qp_attr(struct smc_link *lnk)
IB_QP_DEST_QPN,
&init_attr);

- lnk->wr_tx_cnt = min_t(size_t, SMC_WR_BUF_CNT,
+ lnk->wr_tx_cnt = min_t(size_t, lnk->lgr->max_send_wr,
lnk->qp_attr.cap.max_send_wr);
- lnk->wr_rx_cnt = min_t(size_t, SMC_WR_BUF_CNT * 3,
+ lnk->wr_rx_cnt = min_t(size_t, lnk->lgr->max_recv_wr,
lnk->qp_attr.cap.max_recv_wr);
}

@@ -741,50 +742,51 @@ int smc_wr_alloc_lgr_mem(struct smc_link_group *lgr)
int smc_wr_alloc_link_mem(struct smc_link *link)
{
/* allocate link related memory */
- link->wr_tx_bufs = kcalloc(SMC_WR_BUF_CNT, SMC_WR_BUF_SIZE, GFP_KERNEL);
+ link->wr_tx_bufs = kcalloc(link->lgr->max_send_wr,
+ SMC_WR_BUF_SIZE, GFP_KERNEL);
if (!link->wr_tx_bufs)
goto no_mem;
- link->wr_rx_bufs = kcalloc(SMC_WR_BUF_CNT * 3, link->wr_rx_buflen,
+ link->wr_rx_bufs = kcalloc(link->lgr->max_recv_wr, link->wr_rx_buflen,
GFP_KERNEL);
if (!link->wr_rx_bufs)
goto no_mem_wr_tx_bufs;
- link->wr_tx_ibs = kcalloc(SMC_WR_BUF_CNT, sizeof(link->wr_tx_ibs[0]),
- GFP_KERNEL);
+ link->wr_tx_ibs = kcalloc(link->lgr->max_send_wr,
+ sizeof(link->wr_tx_ibs[0]), GFP_KERNEL);
if (!link->wr_tx_ibs)
goto no_mem_wr_rx_bufs;
- link->wr_rx_ibs = kcalloc(SMC_WR_BUF_CNT * 3,
+ link->wr_rx_ibs = kcalloc(link->lgr->max_recv_wr,
sizeof(link->wr_rx_ibs[0]),
GFP_KERNEL);
if (!link->wr_rx_ibs)
goto no_mem_wr_tx_ibs;
- link->wr_tx_rdmas = kcalloc(SMC_WR_BUF_CNT,
+ link->wr_tx_rdmas = kcalloc(link->lgr->max_send_wr,
sizeof(link->wr_tx_rdmas[0]),
GFP_KERNEL);
if (!link->wr_tx_rdmas)
goto no_mem_wr_rx_ibs;
- link->wr_tx_rdma_sges = kcalloc(SMC_WR_BUF_CNT,
+ link->wr_tx_rdma_sges = kcalloc(link->lgr->max_send_wr,
sizeof(link->wr_tx_rdma_sges[0]),
GFP_KERNEL);
if (!link->wr_tx_rdma_sges)
goto no_mem_wr_tx_rdmas;
- link->wr_tx_sges = kcalloc(SMC_WR_BUF_CNT, sizeof(link->wr_tx_sges[0]),
+ link->wr_tx_sges = kcalloc(link->lgr->max_send_wr, sizeof(link->wr_tx_sges[0]),
GFP_KERNEL);
if (!link->wr_tx_sges)
goto no_mem_wr_tx_rdma_sges;
- link->wr_rx_sges = kcalloc(SMC_WR_BUF_CNT * 3,
+ link->wr_rx_sges = kcalloc(link->lgr->max_recv_wr,
sizeof(link->wr_rx_sges[0]) * link->wr_rx_sge_cnt,
GFP_KERNEL);
if (!link->wr_rx_sges)
goto no_mem_wr_tx_sges;
- link->wr_tx_mask = bitmap_zalloc(SMC_WR_BUF_CNT, GFP_KERNEL);
+ link->wr_tx_mask = bitmap_zalloc(link->lgr->max_send_wr, GFP_KERNEL);
if (!link->wr_tx_mask)
goto no_mem_wr_rx_sges;
- link->wr_tx_pends = kcalloc(SMC_WR_BUF_CNT,
+ link->wr_tx_pends = kcalloc(link->lgr->max_send_wr,
sizeof(link->wr_tx_pends[0]),
GFP_KERNEL);
if (!link->wr_tx_pends)
goto no_mem_wr_tx_mask;
- link->wr_tx_compl = kcalloc(SMC_WR_BUF_CNT,
+ link->wr_tx_compl = kcalloc(link->lgr->max_send_wr,
sizeof(link->wr_tx_compl[0]),
GFP_KERNEL);
if (!link->wr_tx_compl)
@@ -905,7 +907,7 @@ int smc_wr_create_link(struct smc_link *lnk)
goto dma_unmap;
}
smc_wr_init_sge(lnk);
- bitmap_zero(lnk->wr_tx_mask, SMC_WR_BUF_CNT);
+ bitmap_zero(lnk->wr_tx_mask, lnk->lgr->max_send_wr);
init_waitqueue_head(&lnk->wr_tx_wait);
rc = percpu_ref_init(&lnk->wr_tx_refs, smcr_wr_tx_refs_free, 0, GFP_KERNEL);
if (rc)
diff --git a/net/smc/smc_wr.h b/net/smc/smc_wr.h
index f3008dda222a..aa4533af9122 100644
--- a/net/smc/smc_wr.h
+++ b/net/smc/smc_wr.h
@@ -19,8 +19,6 @@
#include "smc.h"
#include "smc_core.h"

-#define SMC_WR_BUF_CNT 16 /* # of ctrl buffers per link */
-
#define SMC_WR_TX_WAIT_FREE_SLOT_TIME (10 * HZ)

#define SMC_WR_TX_SIZE 44 /* actual size of wr_send data (<=SMC_WR_BUF_SIZE) */
--
2.48.1