From patchwork Thu Feb 2 08:26:40 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "D. Wythe" X-Patchwork-Id: 13125508 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3047C63797 for ; Thu, 2 Feb 2023 08:27:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230226AbjBBI1G (ORCPT ); Thu, 2 Feb 2023 03:27:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42372 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232111AbjBBI1E (ORCPT ); Thu, 2 Feb 2023 03:27:04 -0500 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E9D74841BF; Thu, 2 Feb 2023 00:27:02 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=alibuda@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0Vak2b-x_1675326420; Received: from j66a10360.sqa.eu95.tbsite.net(mailfrom:alibuda@linux.alibaba.com fp:SMTPD_---0Vak2b-x_1675326420) by smtp.aliyun-inc.com; Thu, 02 Feb 2023 16:27:00 +0800 From: "D. Wythe" To: kgraul@linux.ibm.com, wenjia@linux.ibm.com, jaka@linux.ibm.com Cc: kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org, "D. Wythe" Subject: [net-next v7 2/4] net/smc: use read semaphores to reduce unnecessary blocking in smc_buf_create() & smcr_buf_unuse() Date: Thu, 2 Feb 2023 16:26:40 +0800 Message-Id: <1675326402-109943-3-git-send-email-alibuda@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1675326402-109943-1-git-send-email-alibuda@linux.alibaba.com> References: <1675326402-109943-1-git-send-email-alibuda@linux.alibaba.com> Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org From: "D. Wythe" 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 --- 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 22ddce6..10a9e09 100644 --- a/net/smc/smc_core.c +++ b/net/smc/smc_core.c @@ -1106,10 +1106,10 @@ 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); } } @@ -2247,7 +2247,7 @@ 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]; @@ -2260,7 +2260,7 @@ 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;