From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from out30-112.freemail.mail.aliyun.com (out30-112.freemail.mail.aliyun.com [115.124.30.112]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5108519F; Wed, 15 Nov 2023 22:18:14 -0800 (PST) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=dust.li@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0VwV9lei_1700115491; Received: from localhost(mailfrom:dust.li@linux.alibaba.com fp:SMTPD_---0VwV9lei_1700115491) by smtp.aliyun-inc.com; Thu, 16 Nov 2023 14:18:12 +0800 Date: Thu, 16 Nov 2023 14:18:11 +0800 From: Dust Li To: Li RongQing , wenjia@linux.ibm.co, netdev@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [PATCH][net-next] net/smc: avoid atomic_set and smp_wmb in the tx path when possible Message-ID: <20231116061811.GC121324@linux.alibaba.com> Reply-To: dust.li@linux.alibaba.com References: <20231116022041.51959-1-lirongqing@baidu.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231116022041.51959-1-lirongqing@baidu.com> On Thu, Nov 16, 2023 at 10:20:41AM +0800, Li RongQing wrote: >there is rare possibility that conn->tx_pushing is not 1, since >tx_pushing is just checked with 1, so move the setting tx_pushing >to 1 after atomic_dec_and_test() return false, to avoid atomic_set >and smp_wmb in tx path > >Signed-off-by: Li RongQing Reviewed-by: Dust Li >--- > net/smc/smc_tx.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > >diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c >index 3b0ff3b..72dbdee 100644 >--- a/net/smc/smc_tx.c >+++ b/net/smc/smc_tx.c >@@ -667,8 +667,6 @@ int smc_tx_sndbuf_nonempty(struct smc_connection *conn) > return 0; > > again: >- atomic_set(&conn->tx_pushing, 1); >- smp_wmb(); /* Make sure tx_pushing is 1 before real send */ > rc = __smc_tx_sndbuf_nonempty(conn); > > /* We need to check whether someone else have added some data into >@@ -677,8 +675,11 @@ int smc_tx_sndbuf_nonempty(struct smc_connection *conn) > * If so, we need to push again to prevent those data hang in the send > * queue. > */ >- if (unlikely(!atomic_dec_and_test(&conn->tx_pushing))) >+ if (unlikely(!atomic_dec_and_test(&conn->tx_pushing))) { >+ atomic_set(&conn->tx_pushing, 1); >+ smp_wmb(); /* Make sure tx_pushing is 1 before real send */ nit: it would be better if we change the comments to "send again". Thanks > goto again; >+ } > > return rc; > } >-- >2.9.4