diff mbox series

[net-next,v4,06/10] net/smc: use read semaphores to reduce unnecessary blocking in smc_buf_create() & smcr_buf_unuse()

Message ID 1666529042-40828-7-git-send-email-alibuda@linux.alibaba.com (mailing list archive)
State Awaiting Upstream
Delegated to: Netdev Maintainers
Headers show
Series optimize the parallelism of SMC-R connections | expand

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Context Check Description
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers warning 2 maintainers not CCed: edumazet@google.com pabeni@redhat.com
netdev/build_clang success Errors and warnings before: 0 this patch: 0
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 28 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

D. Wythe Oct. 23, 2022, 12:43 p.m. UTC 
From: "D. Wythe" <alibuda@linux.alibaba.com>

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@linux.alibaba.com>
---
 net/smc/smc_core.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index b14ad32..48ad76b 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1383,10 +1383,10 @@  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);
 		}
 	}
@@ -2585,7 +2585,7 @@  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];
 
@@ -2598,7 +2598,7 @@  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;