From: "D. Wythe" <alibuda@xxxxxxxxxxxxxxxxx>
Following is part of Off-CPU graph during frequent SMC-R short-lived
processing:
process_one_work (51.19%)
smc_close_passive_work (28.36%)
smcr_buf_unuse (28.34%)
rwsem_down_write_slowpath (28.22%)
smc_listen_work (22.83%)
smc_clc_wait_msg (1.84%)
smc_buf_create (20.45%)
smcr_buf_map_usable_links
rwsem_down_write_slowpath (20.43%)
smcr_lgr_reg_rmbs (0.53%)
rwsem_down_write_slowpath (0.43%)
smc_llc_do_confirm_rkey (0.08%)
We can clearly see that during the connection establishment time,
waiting time of connections is not on IO, but on llc_conf_mutex.
What is more important, the core critical area (smcr_buf_unuse() &
smc_buf_create()) only perfroms read semantics on links, we can
easily replace it with read semaphore.
Signed-off-by: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx>
---
net/smc/smc_core.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index 10a90bf..217d83d2 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1388,10 +1388,10 @@ static void smcr_buf_unuse(struct smc_buf_desc *buf_desc, bool is_rmb,
rc = smc_llc_flow_initiate(lgr, SMC_LLC_FLOW_RKEY);
if (!rc) {
/* protect against smc_llc_cli_rkey_exchange() */
- down_write(&lgr->llc_conf_mutex);
+ down_read(&lgr->llc_conf_mutex);
smc_llc_do_delete_rkey(lgr, buf_desc);
buf_desc->is_conf_rkey = false;
- up_write(&lgr->llc_conf_mutex);
+ up_read(&lgr->llc_conf_mutex);
smc_llc_flow_stop(lgr, &lgr->llc_flow_lcl);
}
}
@@ -2645,7 +2645,7 @@ static int smcr_buf_map_usable_links(struct smc_link_group *lgr,
int i, rc = 0, cnt = 0;
/* protect against parallel link reconfiguration */
- down_write(&lgr->llc_conf_mutex);
+ down_read(&lgr->llc_conf_mutex);
for (i = 0; i < SMC_LINKS_PER_LGR_MAX; i++) {
struct smc_link *lnk = &lgr->lnk[i];
@@ -2658,7 +2658,7 @@ static int smcr_buf_map_usable_links(struct smc_link_group *lgr,
cnt++;
}
out:
- up_write(&lgr->llc_conf_mutex);
+ up_read(&lgr->llc_conf_mutex);
if (!rc && !cnt)
rc = -EINVAL;
return rc;
--
1.8.3.1
