From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752661AbdBCVUa (ORCPT ); Fri, 3 Feb 2017 16:20:30 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:34279 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752331AbdBCVU2 (ORCPT ); Fri, 3 Feb 2017 16:20:28 -0500 Subject: Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check for tx enable To: Eric Dumazet References: <1486143755-192532-1-git-send-email-shannon.nelson@oracle.com> <1486143755-192532-6-git-send-email-shannon.nelson@oracle.com> <1486144585.21871.92.camel@edumazet-glaptop3.roam.corp.google.com> Cc: netdev@vger.kernel.org, davem@davemloft.net, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org From: Shannon Nelson Organization: Oracle Corporation Message-ID: Date: Fri, 3 Feb 2017 13:20:43 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <1486144585.21871.92.camel@edumazet-glaptop3.roam.corp.google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/3/2017 9:56 AM, Eric Dumazet wrote: > On Fri, 2017-02-03 at 09:42 -0800, Shannon Nelson wrote: >> In order to allow the underlying LDC and outstanding memory operations >> to potentially catch up with the driver's Tx requests, add a memory >> barrier before checking again for available tx descriptors. >> >> Signed-off-by: Shannon Nelson >> --- >> drivers/net/ethernet/sun/sunvnet_common.c | 1 + >> 1 files changed, 1 insertions(+), 0 deletions(-) >> >> diff --git a/drivers/net/ethernet/sun/sunvnet_common.c b/drivers/net/ethernet/sun/sunvnet_common.c >> index 5d0d386..98e758e 100644 >> --- a/drivers/net/ethernet/sun/sunvnet_common.c >> +++ b/drivers/net/ethernet/sun/sunvnet_common.c >> @@ -1467,6 +1467,7 @@ ldc_start_done: >> dr->prod = (dr->prod + 1) & (VNET_TX_RING_SIZE - 1); >> if (unlikely(vnet_tx_dring_avail(dr) < 1)) { >> netif_tx_stop_queue(txq); >> + dma_wmb(); > > This does not look right. > > I believe you need smp_rmb() here. Well, it probably should be dma_rmb(), since regardless of the number of cores we think we have, we're communicating with a peer ldom that has its own core(s). Either way, on sparc they all seem to boil down to the same bit of asm, but using the "rmb" part makes more logical sense. I'll respin with dma_rmb(). Good catch, thanks, sln > >> if (vnet_tx_dring_avail(dr) > VNET_TX_WAKEUP_THRESH(dr)) >> netif_tx_wake_queue(txq); >> } > >