[PATCH net-next v2 2/2] net/smc: rdma write inline if qp has sufficient inline space

Guangguan Wang
2022-05-14T10:28:15Z

Rdma write with inline flag when sending small packages,
whose length is shorter than the qp's max_inline_data, can
help reducing latency.

In my test environment, which are 2 VMs running on the same
physical host and whose NICs(ConnectX-4Lx) are working on
SR-IOV mode, qperf shows 0.5us-0.7us improvement in latency.

Test command:
server: smc_run taskset -c 1 qperf
client: smc_run taskset -c 1 qperf <server ip> -oo \
msg_size:1:2K:*2 -t 30 -vu tcp_lat

The results shown below:
msgsize before after
1B 11.2 us 10.6 us (-0.6 us)
2B 11.2 us 10.7 us (-0.5 us)
4B 11.3 us 10.7 us (-0.6 us)
8B 11.2 us 10.6 us (-0.6 us)
16B 11.3 us 10.7 us (-0.6 us)
32B 11.3 us 10.6 us (-0.7 us)
64B 11.2 us 11.2 us (0 us)
128B 11.2 us 11.2 us (0 us)
256B 11.2 us 11.2 us (0 us)
512B 11.4 us 11.3 us (-0.1 us)
1KB 11.4 us 11.5 us (0.1 us)
2KB 11.5 us 11.5 us (0 us)

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
---
net/smc/smc_tx.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 98ca9229fe87..805a546e8c04 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -391,12 +391,20 @@ static int smcr_tx_rdma_writes(struct smc_connection *conn, size_t len,
int rc;

for (dstchunk = 0; dstchunk < 2; dstchunk++) {
- struct ib_sge *sge =
- wr_rdma_buf->wr_tx_rdma[dstchunk].wr.sg_list;
+ struct ib_rdma_wr *wr = &wr_rdma_buf->wr_tx_rdma[dstchunk];
+ struct ib_sge *sge = wr->wr.sg_list;
+ u64 base_addr = dma_addr;
+
+ if (dst_len < link->qp_attr.cap.max_inline_data) {
+ base_addr = (uintptr_t)conn->sndbuf_desc->cpu_addr;
+ wr->wr.send_flags |= IB_SEND_INLINE;
+ } else {
+ wr->wr.send_flags &= ~IB_SEND_INLINE;
+ }

num_sges = 0;
for (srcchunk = 0; srcchunk < 2; srcchunk++) {
- sge[srcchunk].addr = dma_addr + src_off;
+ sge[srcchunk].addr = base_addr + src_off;
sge[srcchunk].length = src_len;
num_sges++;

@@ -410,8 +418,7 @@ static int smcr_tx_rdma_writes(struct smc_connection *conn, size_t len,
src_len = dst_len - src_len; /* remainder */
src_len_sum += src_len;
}
- rc = smc_tx_rdma_write(conn, dst_off, num_sges,
- &wr_rdma_buf->wr_tx_rdma[dstchunk]);
+ rc = smc_tx_rdma_write(conn, dst_off, num_sges, wr);
if (rc)
return rc;
if (dst_len_sum == len)
--
2.24.3 (Apple Git-128)