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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 24086C3279B for ; Wed, 11 Jul 2018 01:09:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1976208AD for ; Wed, 11 Jul 2018 01:09:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D1976208AD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732401AbeGKBLC (ORCPT ); Tue, 10 Jul 2018 21:11:02 -0400 Received: from mga04.intel.com ([192.55.52.120]:44237 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732278AbeGKBLC (ORCPT ); Tue, 10 Jul 2018 21:11:02 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Jul 2018 18:09:20 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,336,1526367600"; d="scan'208";a="215011065" Received: from debian.sh.intel.com (HELO debian) ([10.67.104.228]) by orsmga004.jf.intel.com with ESMTP; 10 Jul 2018 18:09:18 -0700 Date: Wed, 11 Jul 2018 09:09:05 +0800 From: Tiwei Bie To: Jason Wang Cc: mst@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, virtio-dev@lists.oasis-open.org, wexu@redhat.com, jfreimann@redhat.com Subject: Re: [virtio-dev] Re: [PATCH net-next v1 4/5] virtio_ring: add event idx support in packed ring Message-ID: <20180711010905.GB28235@debian> References: <20180709072241.8886-1-tiwei.bie@intel.com> <20180709072241.8886-5-tiwei.bie@intel.com> <9ee31221-9f4a-f1c5-0f0b-8d178bb536e9@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9ee31221-9f4a-f1c5-0f0b-8d178bb536e9@redhat.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 10, 2018 at 01:50:03PM +0800, Jason Wang wrote: > On 2018年07月09日 15:22, Tiwei Bie wrote: > > @@ -1059,9 +1059,19 @@ static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq) > > * suppressions. */ > > virtio_mb(vq->weak_barriers); > > + old = vq->next_avail_idx - vq->num_added; > > + new = vq->next_avail_idx; > > + vq->num_added = 0; > > + > > snapshot = *(u32 *)vq->vring_packed.device; > > I think we should use READ_ONCE() to prevent compiler from re-reading. I'll do it. Thanks! Best regards, Tiwei Bie > > > + off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot & 0xffff)); > > flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; > > + wrap_counter = off_wrap >> 15; > > + event_idx = off_wrap & ~(1 << 15); > > + if (wrap_counter != vq->avail_wrap_counter) > > + event_idx -= vq->vring_packed.num; > > Thanks >