From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751032AbcB2FR3 (ORCPT ); Mon, 29 Feb 2016 00:17:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43496 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbcB2FR2 (ORCPT ); Mon, 29 Feb 2016 00:17:28 -0500 Subject: Re: [PATCH V3 3/3] vhost_net: basic polling support To: Christian Borntraeger , kvm@vger.kernel.org, mst@redhat.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <1456476164-17242-1-git-send-email-jasowang@redhat.com> <1456476164-17242-4-git-send-email-jasowang@redhat.com> <56D36D25.6070903@de.ibm.com> Cc: RAPOPORT@il.ibm.com, yang.zhang.wz@gmail.com From: Jason Wang Message-ID: <56D3D45B.3020600@redhat.com> Date: Mon, 29 Feb 2016 13:17:15 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <56D36D25.6070903@de.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/29/2016 05:56 AM, Christian Borntraeger wrote: > On 02/26/2016 09:42 AM, Jason Wang wrote: >> > This patch tries to poll for new added tx buffer or socket receive >> > queue for a while at the end of tx/rx processing. The maximum time >> > spent on polling were specified through a new kind of vring ioctl. >> > >> > Signed-off-by: Jason Wang >> > --- >> > drivers/vhost/net.c | 79 +++++++++++++++++++++++++++++++++++++++++++--- >> > drivers/vhost/vhost.c | 14 ++++++++ >> > drivers/vhost/vhost.h | 1 + >> > include/uapi/linux/vhost.h | 6 ++++ >> > 4 files changed, 95 insertions(+), 5 deletions(-) >> > >> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c >> > index 9eda69e..c91af93 100644 >> > --- a/drivers/vhost/net.c >> > +++ b/drivers/vhost/net.c >> > @@ -287,6 +287,44 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) >> > rcu_read_unlock_bh(); >> > } >> > >> > +static inline unsigned long busy_clock(void) >> > +{ >> > + return local_clock() >> 10; >> > +} >> > + >> > +static bool vhost_can_busy_poll(struct vhost_dev *dev, >> > + unsigned long endtime) >> > +{ >> > + return likely(!need_resched()) && >> > + likely(!time_after(busy_clock(), endtime)) && >> > + likely(!signal_pending(current)) && >> > + !vhost_has_work(dev) && >> > + single_task_running(); >> > +} >> > + >> > +static int vhost_net_tx_get_vq_desc(struct vhost_net *net, >> > + struct vhost_virtqueue *vq, >> > + struct iovec iov[], unsigned int iov_size, >> > + unsigned int *out_num, unsigned int *in_num) >> > +{ >> > + unsigned long uninitialized_var(endtime); >> > + int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), >> > + out_num, in_num, NULL, NULL); >> > + >> > + if (r == vq->num && vq->busyloop_timeout) { >> > + preempt_disable(); >> > + endtime = busy_clock() + vq->busyloop_timeout; >> > + while (vhost_can_busy_poll(vq->dev, endtime) && >> > + vhost_vq_avail_empty(vq->dev, vq)) >> > + cpu_relax(); > Can you use cpu_relax_lowlatency (which should be the same as cpu_relax for almost > everybody but s390? cpu_relax (without low latency might give up the time slice > when running under another hypervisor (like LPAR on s390), which might not be what > we want here. Ok, will do this in next version.