From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763195Ab3IECy5 (ORCPT ); Wed, 4 Sep 2013 22:54:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39300 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759510Ab3IECyz (ORCPT ); Wed, 4 Sep 2013 22:54:55 -0400 Message-ID: <5227F274.9040506@redhat.com> Date: Thu, 05 Sep 2013 10:54:44 +0800 From: Jason Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130803 Thunderbird/17.0.8 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3 4/6] vhost_net: determine whether or not to use zerocopy at one time References: <1378111261-14826-1-git-send-email-jasowang@redhat.com> <1378111261-14826-5-git-send-email-jasowang@redhat.com> <20130904115929.GA9393@redhat.com> In-Reply-To: <20130904115929.GA9393@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/04/2013 07:59 PM, Michael S. Tsirkin wrote: > On Mon, Sep 02, 2013 at 04:40:59PM +0800, Jason Wang wrote: >> Currently, even if the packet length is smaller than VHOST_GOODCOPY_LEN, if >> upend_idx != done_idx we still set zcopy_used to true and rollback this choice >> later. This could be avoided by determining zerocopy once by checking all >> conditions at one time before. >> >> Signed-off-by: Jason Wang >> --- >> drivers/vhost/net.c | 47 ++++++++++++++++++++--------------------------- >> 1 files changed, 20 insertions(+), 27 deletions(-) >> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c >> index 8a6dd0d..3f89dea 100644 >> --- a/drivers/vhost/net.c >> +++ b/drivers/vhost/net.c >> @@ -404,43 +404,36 @@ static void handle_tx(struct vhost_net *net) >> iov_length(nvq->hdr, s), hdr_size); >> break; >> } >> - zcopy_used = zcopy && (len >= VHOST_GOODCOPY_LEN || >> - nvq->upend_idx != nvq->done_idx); >> + >> + zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN >> + && (nvq->upend_idx + 1) % UIO_MAXIOV != >> + nvq->done_idx > Thinking about this, this looks strange. > The original idea was that once we start doing zcopy, we keep > using the heads ring even for short packets until no zcopy is outstanding. What's the reason for keep using the heads ring? > > What's the logic behind (nvq->upend_idx + 1) % UIO_MAXIOV != nvq->done_idx > here? Because we initialize both upend_idx and done_idx to zero, so upend_idx != done_idx could not be used to check whether or not the heads ring were full. >> + && vhost_net_tx_select_zcopy(net); >> >> /* use msg_control to pass vhost zerocopy ubuf info to skb */ >> if (zcopy_used) { >> + struct ubuf_info *ubuf; >> + ubuf = nvq->ubuf_info + nvq->upend_idx; >> + >> vq->heads[nvq->upend_idx].id = head; >> - if (!vhost_net_tx_select_zcopy(net) || >> - len < VHOST_GOODCOPY_LEN) { >> - /* copy don't need to wait for DMA done */ >> - vq->heads[nvq->upend_idx].len = >> - VHOST_DMA_DONE_LEN; >> - msg.msg_control = NULL; >> - msg.msg_controllen = 0; >> - ubufs = NULL; >> - } else { >> - struct ubuf_info *ubuf; >> - ubuf = nvq->ubuf_info + nvq->upend_idx; >> - >> - vq->heads[nvq->upend_idx].len = >> - VHOST_DMA_IN_PROGRESS; >> - ubuf->callback = vhost_zerocopy_callback; >> - ubuf->ctx = nvq->ubufs; >> - ubuf->desc = nvq->upend_idx; >> - msg.msg_control = ubuf; >> - msg.msg_controllen = sizeof(ubuf); >> - ubufs = nvq->ubufs; >> - kref_get(&ubufs->kref); >> - } >> + vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS; >> + ubuf->callback = vhost_zerocopy_callback; >> + ubuf->ctx = nvq->ubufs; >> + ubuf->desc = nvq->upend_idx; >> + msg.msg_control = ubuf; >> + msg.msg_controllen = sizeof(ubuf); >> + ubufs = nvq->ubufs; >> + kref_get(&ubufs->kref); >> nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV; >> - } else >> + } else { >> msg.msg_control = NULL; >> + ubufs = NULL; >> + } >> /* TODO: Check specific error and bomb out unless ENOBUFS? */ >> err = sock->ops->sendmsg(NULL, sock, &msg, len); >> if (unlikely(err < 0)) { >> if (zcopy_used) { >> - if (ubufs) >> - vhost_net_ubuf_put(ubufs); >> + vhost_net_ubuf_put(ubufs); >> nvq->upend_idx = ((unsigned)nvq->upend_idx - 1) >> % UIO_MAXIOV; >> } >> -- >> 1.7.1 > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html