Re: [dpdk-dev] [PATCH v4 09/10] net/ifc: support SW assisted VDPA live migration

["Wang, Xiao W" <xiao.w.wang@intel.com>]

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Sunday, December 16, 2018 1:35 AM
> To: Wang, Xiao W <xiao.w.wang@intel.com>; Bie, Tiwei <tiwei.bie@intel.com>
> Cc: alejandro.lucero@netronome.com; dev@dpdk.org; Wang, Zhihong
> <zhihong.wang@intel.com>; Ye, Xiaolong <xiaolong.ye@intel.com>
> Subject: Re: [PATCH v4 09/10] net/ifc: support SW assisted VDPA live migration
> 
> 
> 
> On 12/14/18 10:16 PM, Xiao Wang wrote:
> > In SW assisted live migration mode, driver will stop the device and
> > setup a mediate virtio ring to relay the communication between the
> > virtio driver and the VDPA device.
> >
> > This data path intervention will allow SW to help on guest dirty page
> > logging for live migration.
> >
> > This SW fallback is event driven relay thread, so when the network
> > throughput is low, this SW fallback will take little CPU resource, but
> > when the throughput goes up, the relay thread's CPU usage will goes up
> > accordinly.
> 
> s/accordinly/accordingly/
> 

Will fix it in next version.

> >
> > User needs to take all the factors including CPU usage, guest perf
> > degradation, etc. into consideration when selecting the live migration
> > support mode.
> >
> > Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
> > ---
> >   drivers/net/ifc/base/ifcvf.h |   1 +
> >   drivers/net/ifc/ifcvf_vdpa.c | 346
> ++++++++++++++++++++++++++++++++++++++++++-
> >   2 files changed, 344 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/ifc/base/ifcvf.h b/drivers/net/ifc/base/ifcvf.h
> > index c15c69107..e8a30d2c6 100644
> > --- a/drivers/net/ifc/base/ifcvf.h
> > +++ b/drivers/net/ifc/base/ifcvf.h
> > @@ -50,6 +50,7 @@
> >   #define IFCVF_LM_ENABLE_VF		0x1
> >   #define IFCVF_LM_ENABLE_PF		0x3
> >   #define IFCVF_LOG_BASE			0x100000000000
> > +#define IFCVF_MEDIATE_VRING		0x200000000000
> 
> MEDIATED?

"mediate" is used as adjective here.

> 
> >
> >   #define IFCVF_32_BIT_MASK		0xffffffff
> >
> > diff --git a/drivers/net/ifc/ifcvf_vdpa.c b/drivers/net/ifc/ifcvf_vdpa.c
> > index f181c5a6e..61757d0b4 100644
> > --- a/drivers/net/ifc/ifcvf_vdpa.c
> > +++ b/drivers/net/ifc/ifcvf_vdpa.c
> > @@ -63,6 +63,9 @@ struct ifcvf_internal {
> >   	rte_atomic32_t running;
> >   	rte_spinlock_t lock;
> >   	bool sw_lm;

[...]

> > +static void *
> > +vring_relay(void *arg)
> > +{
> > +	int i, vid, epfd, fd, nfds;
> > +	struct ifcvf_internal *internal = (struct ifcvf_internal *)arg;
> > +	struct rte_vhost_vring vring;
> > +	struct rte_intr_handle *intr_handle;
> > +	uint16_t qid, q_num;
> > +	struct epoll_event events[IFCVF_MAX_QUEUES * 4];
> > +	struct epoll_event ev;
> > +	int nbytes;
> > +	uint64_t buf;
> > +
> > +	vid = internal->vid;
> > +	q_num = rte_vhost_get_vring_num(vid);
> > +	/* prepare the mediate vring */
> > +	for (qid = 0; qid < q_num; qid++) {
> > +		rte_vhost_get_vring_base(vid, qid,
> > +				&internal->m_vring[qid].avail->idx,
> > +				&internal->m_vring[qid].used->idx);
> > +		rte_vdpa_relay_vring_avail(vid, qid, &internal->m_vring[qid]);
> > +	}
> > +
> > +	/* add notify fd and interrupt fd to epoll */
> > +	epfd = epoll_create(IFCVF_MAX_QUEUES * 2);
> > +	if (epfd < 0) {
> > +		DRV_LOG(ERR, "failed to create epoll instance.");
> > +		return NULL;
> > +	}
> > +	internal->epfd = epfd;
> > +
> > +	for (qid = 0; qid < q_num; qid++) {
> > +		ev.events = EPOLLIN | EPOLLPRI;
> > +		rte_vhost_get_vhost_vring(vid, qid, &vring);
> > +		ev.data.u64 = qid << 1 | (uint64_t)vring.kickfd << 32;
> > +		if (epoll_ctl(epfd, EPOLL_CTL_ADD, vring.kickfd, &ev) < 0) {
> > +			DRV_LOG(ERR, "epoll add error: %s", strerror(errno));
> > +			return NULL;
> > +		}
> > +	}
> > +
> > +	intr_handle = &internal->pdev->intr_handle;
> > +	for (qid = 0; qid < q_num; qid++) {
> > +		ev.events = EPOLLIN | EPOLLPRI;
> > +		ev.data.u64 = 1 | qid << 1 |
> > +			(uint64_t)intr_handle->efds[qid] << 32;
> > +		if (epoll_ctl(epfd, EPOLL_CTL_ADD, intr_handle->efds[qid],
> &ev)
> > +				< 0) {
> > +			DRV_LOG(ERR, "epoll add error: %s", strerror(errno));
> > +			return NULL;
> > +		}
> > +	}
> > +
> > +	/* start relay with a first kick */
> > +	for (qid = 0; qid < q_num; qid++)
> > +		ifcvf_notify_queue(&internal->hw, qid);
> > +
> > +	/* listen to the events and react accordingly */
> > +	for (;;) {
> > +		nfds = epoll_wait(epfd, events, q_num * 2, -1);
> > +		if (nfds < 0) {
> > +			if (errno == EINTR)
> > +				continue;
> > +			DRV_LOG(ERR, "epoll_wait return fail\n");
> > +			return NULL;
> > +		}
> > +
> > +		for (i = 0; i < nfds; i++) {
> > +			fd = (uint32_t)(events[i].data.u64 >> 32);
> > +			do {
> > +				nbytes = read(fd, &buf, 8);
> > +				if (nbytes < 0) {
> > +					if (errno == EINTR ||
> > +					    errno == EWOULDBLOCK ||
> > +					    errno == EAGAIN)
> > +						continue;
> > +					DRV_LOG(INFO, "Error reading "
> > +						"kickfd: %s",
> > +						strerror(errno));
> > +				}
> > +				break;
> > +			} while (1);
> > +
> > +			qid = events[i].data.u32 >> 1;
> > +
> > +			if (events[i].data.u32 & 1)
> > +				update_used_ring(internal, qid);
> > +			else
> > +				update_avail_ring(internal, qid);
> > +		}
> > +	}
> > +
> > +	return NULL;
> > +}
> > +
> > +static int
> > +setup_vring_relay(struct ifcvf_internal *internal)
> > +{
> > +	int ret;
> > +
> > +	ret = pthread_create(&internal->tid, NULL, vring_relay,
> > +			(void *)internal);
> 
> So it will be scheduled without any affinity?
> Shouldn't it use a pmd thread instead?

The new thread will inherit the thread affinity from its parent thread. As you know, vdpa is trying to
 minimize CPU usage for virtio HW acceleration, and we assign just one core to vdpa daemon
 (doc/guides/sample_app_ug/vdpa.rst), so there's no dedicated pmd worker core.

Thanks,
Xiao