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Message-Id: <46f364ce7878b740e58bf44d3bed5fe23c64a260.1660152975.git.alibuda@linux.alibaba.com> Date: Thu, 11 Aug 2022 01:47:38 +0800 From: "D. Wythe" <alibuda@...ux.alibaba.com> To: kgraul@...ux.ibm.com, wenjia@...ux.ibm.com Cc: kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org, linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org Subject: [PATCH net-next 07/10] net/smc: reduce unnecessary blocking in smcr_lgr_reg_rmbs() From: "D. Wythe" <alibuda@...ux.alibaba.com> Unlike smc_buf_create() and smcr_buf_unuse(), smcr_lgr_reg_rmbs() is exclusive when assigned rmb_desc was not registered, although it can be executed in parallel when assigned rmb_desc was registered already and only performs read semtamics on it. Hence, we can not simply replace it with read semaphore. The idea here is that if the assigned rmb_desc was registered already, use read semaphore to protect the critical section, once the assigned rmb_desc was not registered, keep using keep write semaphore still to keep its exclusivity. Thanks to the reusable features of rmb_desc, which allows us to execute in parallel in most cases. Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com> --- net/smc/af_smc.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c index 51b90e2..39dbf39 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -516,10 +516,25 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link, { struct smc_link_group *lgr = link->lgr; int i, rc = 0; + bool slow = false; rc = smc_llc_flow_initiate(lgr, SMC_LLC_FLOW_RKEY); if (rc) return rc; + + down_read(&lgr->llc_conf_mutex); + for (i = 0; i < SMC_LINKS_PER_LGR_MAX; i++) { + if (!smc_link_active(&lgr->lnk[i])) + continue; + if (!rmb_desc->is_reg_mr[link->link_idx]) { + up_read(&lgr->llc_conf_mutex); + goto slow_path; + } + } + /* mr register already */ + goto fast_path; +slow_path: + slow = true; /* protect against parallel smc_llc_cli_rkey_exchange() and * parallel smcr_link_reg_buf() */ @@ -531,7 +546,7 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link, if (rc) goto out; } - +fast_path: /* exchange confirm_rkey msg with peer */ rc = smc_llc_do_confirm_rkey(link, rmb_desc); if (rc) { @@ -540,7 +555,7 @@ static int smcr_lgr_reg_rmbs(struct smc_link *link, } rmb_desc->is_conf_rkey = true; out: - up_write(&lgr->llc_conf_mutex); + slow ? up_write(&lgr->llc_conf_mutex) : up_read(&lgr->llc_conf_mutex); smc_llc_flow_stop(lgr, &lgr->llc_flow_lcl); return rc; } -- 1.8.3.1
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