From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF1ABC2D0DC for ; Thu, 2 Jan 2020 18:09:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C8B25206E6 for ; Thu, 2 Jan 2020 18:09:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="qhcmRs0/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728064AbgABSJw (ORCPT ); Thu, 2 Jan 2020 13:09:52 -0500 Received: from aserp2120.oracle.com ([141.146.126.78]:46404 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727829AbgABSJv (ORCPT ); Thu, 2 Jan 2020 13:09:51 -0500 Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1]) by aserp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id 002I4UeF103402; Thu, 2 Jan 2020 18:09:42 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type : content-transfer-encoding; s=corp-2019-08-05; bh=7mFri1IvSbR2yII37pLPC48tNxELRWB3ByRsOG8tlYQ=; b=qhcmRs0/QQhxN2gVF4r5l5qW8ef2d7NZxRbTEoIEo+BrmlwVmKBOWbf0ZlNfYqAyI+DM wHyWXhWALkSTMxHzd7qiJpmkCR62AisX9t0iVHcuQ/hZ7K5lZNNZ79AgKm87wcssefrB BSgYqh5qo/4BK6GX0LTYj1cjI7iHyrUrgifHEJeftDWoft2lvO72wE3bdFiwejkubFeA XE65q1zmvH0G/Uy+XxBd177P769cEe43LyR6eDpPqMyVLsyIpYUHsksQ2dnumuXiMeKt yXnaDDgZ+EXQD0OrkayL1Zp9gOxBGN4ebolc10qUPOkAThOl4QlSFLZdHEa3B59rzz2O ng== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by aserp2120.oracle.com with ESMTP id 2x5y0prp6m-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 02 Jan 2020 18:09:41 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id 002I3RoQ013871; Thu, 2 Jan 2020 18:09:41 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3030.oracle.com with ESMTP id 2x9jm6e8hd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 02 Jan 2020 18:09:41 +0000 Received: from abhmp0014.oracle.com (abhmp0014.oracle.com [141.146.116.20]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 002I9d9N022788; Thu, 2 Jan 2020 18:09:40 GMT Received: from Lirans-MBP.Home (/79.178.220.19) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 02 Jan 2020 10:09:39 -0800 From: Liran Alon To: netanel@amazon.com, davem@davemloft.net, netdev@vger.kernel.org Cc: saeedb@amazon.com, zorik@amazon.com, sameehj@amazon.com, igorch@amazon.com, akiyano@amazon.com, evgenys@amazon.com, gtzalik@amazon.com, ndagan@amazon.com, matua@amazon.com, galpress@amazon.com, Liran Alon , =?UTF-8?q?H=C3=A5kon=20Bugge?= Subject: [PATCH 1/2] net: AWS ENA: Remove unncessary wmb() to flush bounce buffer Date: Thu, 2 Jan 2020 20:08:29 +0200 Message-Id: <20200102180830.66676-2-liran.alon@oracle.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200102180830.66676-1-liran.alon@oracle.com> References: <20200102180830.66676-1-liran.alon@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9488 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-2001020151 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9488 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-2001020151 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Current code executes wmb() in order to flush writes to bounce buffer before copying it to device-memory (PCI BAR mapped as WC) to ensure consistent data is written to device-memory. However, this wmb() is unnecessary. This is because all reads from the buffer are guaranteed to be consistent with previous writes to the buffer done from the same task (Which is the only one that writes to the buffer). i.e. If a single CPU runs both the writes to the buffer and the reads from the buffer, the reads are guaranteed to read most up-to-date data in program order (E.g. Due to store-to-load-forwarding mechanism). Otherwise, there is a context-switch, and that should make writes before context-switch globally visible as-well. Reviewed-by: Håkon Bugge Signed-off-by: Liran Alon --- drivers/net/ethernet/amazon/ena/ena_eth_com.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/drivers/net/ethernet/amazon/ena/ena_eth_com.c b/drivers/net/ethernet/amazon/ena/ena_eth_com.c index 2845ac277724..742578ac1240 100644 --- a/drivers/net/ethernet/amazon/ena/ena_eth_com.c +++ b/drivers/net/ethernet/amazon/ena/ena_eth_com.c @@ -93,11 +93,6 @@ static int ena_com_write_bounce_buffer_to_dev(struct ena_com_io_sq *io_sq, io_sq->qid, io_sq->entries_in_tx_burst_left); } - /* Make sure everything was written into the bounce buffer before - * writing the bounce buffer to the device - */ - wmb(); - /* The line is completed. Copy it to dev */ __iowrite64_copy(io_sq->desc_addr.pbuf_dev_addr + dst_offset, bounce_buffer, (llq_info->desc_list_entry_size) / 8); -- 2.20.1