From: "Michael S. Tsirkin" <mst@redhat.com>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>,
Maxime Coquelin <maxime.coquelin@redhat.com>,
huawei.xie@intel.com, dev@dpdk.org, vkaplans@redhat.com
Subject: Re: [dpdk-dev] [PATCH v3] vhost: Add indirect descriptors support to the TX path
Date: Mon, 26 Sep 2016 15:25:35 +0300 [thread overview]
Message-ID: <20160926152442-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20160926030354.GF23158@yliu-dev.sh.intel.com>
On Mon, Sep 26, 2016 at 11:03:54AM +0800, Yuanhan Liu wrote:
> On Fri, Sep 23, 2016 at 01:24:14PM -0700, Stephen Hemminger wrote:
> > On Fri, 23 Sep 2016 21:22:23 +0300
> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >
> > > On Fri, Sep 23, 2016 at 08:16:09PM +0200, Maxime Coquelin wrote:
> > > >
> > > >
> > > > On 09/23/2016 08:06 PM, Michael S. Tsirkin wrote:
> > > > > On Fri, Sep 23, 2016 at 08:02:27PM +0200, Maxime Coquelin wrote:
> > > > > >
> > > > > >
> > > > > > On 09/23/2016 05:49 PM, Michael S. Tsirkin wrote:
> > > > > > > On Fri, Sep 23, 2016 at 10:28:23AM +0200, Maxime Coquelin wrote:
> > > > > > > > Indirect descriptors are usually supported by virtio-net devices,
> > > > > > > > allowing to dispatch a larger number of requests.
> > > > > > > >
> > > > > > > > When the virtio device sends a packet using indirect descriptors,
> > > > > > > > only one slot is used in the ring, even for large packets.
> > > > > > > >
> > > > > > > > The main effect is to improve the 0% packet loss benchmark.
> > > > > > > > A PVP benchmark using Moongen (64 bytes) on the TE, and testpmd
> > > > > > > > (fwd io for host, macswap for VM) on DUT shows a +50% gain for
> > > > > > > > zero loss.
> > > > > > > >
> > > > > > > > On the downside, micro-benchmark using testpmd txonly in VM and
> > > > > > > > rxonly on host shows a loss between 1 and 4%.i But depending on
> > > > > > > > the needs, feature can be disabled at VM boot time by passing
> > > > > > > > indirect_desc=off argument to vhost-user device in Qemu.
> > > > > > >
> > > > > > > Even better, change guest pmd to only use indirect
> > > > > > > descriptors when this makes sense (e.g. sufficiently
> > > > > > > large packets).
> > > > > > With the micro-benchmark, the degradation is quite constant whatever
> > > > > > the packet size.
> > > > > >
> > > > > > For PVP, I could not test with larger packets than 64 bytes, as I don't
> > > > > > have a 40G interface,
> > > > >
> > > > > Don't 64 byte packets fit in a single slot anyway?
> > > > No, indirect is used. I didn't checked in details, but I think this is
> > > > because there is no headroom reserved in the mbuf.
> > > >
> > > > This is the condition to meet to fit in a single slot:
> > > > /* optimize ring usage */
> > > > if (vtpci_with_feature(hw, VIRTIO_F_ANY_LAYOUT) &&
> > > > rte_mbuf_refcnt_read(txm) == 1 &&
> > > > RTE_MBUF_DIRECT(txm) &&
> > > > txm->nb_segs == 1 &&
> > > > rte_pktmbuf_headroom(txm) >= hdr_size &&
> > > > rte_is_aligned(rte_pktmbuf_mtod(txm, char *),
> > > > __alignof__(struct virtio_net_hdr_mrg_rxbuf)))
> > > > can_push = 1;
> > > > else if (vtpci_with_feature(hw, VIRTIO_RING_F_INDIRECT_DESC) &&
> > > > txm->nb_segs < VIRTIO_MAX_TX_INDIRECT)
> > > > use_indirect = 1;
> > > >
> > > > I will check more in details next week.
> > >
> > > Two thoughts then
> > > 1. so can some headroom be reserved?
> > > 2. how about using indirect with 3 s/g entries,
> > > but direct with 2 and down?
> >
> > The default mbuf allocator does keep headroom available. Sounds like a
> > test bug.
>
> That's because we don't have VIRTIO_F_ANY_LAYOUT set, as Stephen claimed
> in v2's comment.
>
> Since DPDK vhost actually supports VIRTIO_F_ANY_LAYOUT for a while, I'd
> like to add it in the features list (VHOST_SUPPORTED_FEATURES).
>
> Will drop a patch shortly.
>
> --yliu
If VERSION_1 is set then this implies ANY_LAYOUT without it being set.
--
MST
next prev parent reply other threads:[~2016-09-26 12:25 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-23 8:28 Maxime Coquelin
2016-09-23 15:49 ` Michael S. Tsirkin
2016-09-23 18:02 ` Maxime Coquelin
2016-09-23 18:06 ` Michael S. Tsirkin
2016-09-23 18:16 ` Maxime Coquelin
2016-09-23 18:22 ` Michael S. Tsirkin
2016-09-23 20:24 ` Stephen Hemminger
2016-09-26 3:03 ` Yuanhan Liu
2016-09-26 12:25 ` Michael S. Tsirkin [this message]
2016-09-26 13:04 ` Yuanhan Liu
2016-09-27 4:15 ` Yuanhan Liu
2016-09-27 7:25 ` Maxime Coquelin
2016-09-27 8:42 ` [dpdk-dev] [PATCH v4] " Maxime Coquelin
2016-09-27 12:18 ` Yuanhan Liu
2016-10-14 7:24 ` Wang, Zhihong
2016-10-14 7:34 ` Wang, Zhihong
2016-10-14 15:50 ` Maxime Coquelin
2016-10-17 11:23 ` Maxime Coquelin
2016-10-17 13:21 ` Yuanhan Liu
2016-10-17 14:14 ` Maxime Coquelin
2016-10-27 9:00 ` Wang, Zhihong
2016-10-27 9:10 ` Maxime Coquelin
2016-10-27 9:55 ` Maxime Coquelin
2016-10-27 10:19 ` Wang, Zhihong
2016-10-28 7:32 ` Pierre Pfister (ppfister)
2016-10-28 7:58 ` Maxime Coquelin
2016-11-01 8:15 ` Yuanhan Liu
2016-11-01 9:39 ` Thomas Monjalon
2016-11-02 2:44 ` Yuanhan Liu
2016-10-27 10:33 ` Yuanhan Liu
2016-10-27 10:35 ` Maxime Coquelin
2016-10-27 10:46 ` Yuanhan Liu
2016-10-28 0:49 ` Wang, Zhihong
2016-10-28 7:42 ` Maxime Coquelin
2016-10-31 10:01 ` Wang, Zhihong
2016-11-02 10:51 ` Maxime Coquelin
2016-11-03 8:11 ` Maxime Coquelin
2016-11-04 6:18 ` Xu, Qian Q
2016-11-04 7:41 ` Maxime Coquelin
2016-11-04 7:20 ` Wang, Zhihong
2016-11-04 7:57 ` Maxime Coquelin
2016-11-04 7:59 ` Maxime Coquelin
2016-11-04 10:43 ` Wang, Zhihong
2016-11-04 11:22 ` Maxime Coquelin
2016-11-04 11:36 ` Yuanhan Liu
2016-11-04 11:39 ` Maxime Coquelin
2016-11-04 12:30 ` Wang, Zhihong
2016-11-04 12:54 ` Maxime Coquelin
2016-11-04 13:09 ` Wang, Zhihong
2016-11-08 10:51 ` Wang, Zhihong
2016-10-27 10:53 ` Maxime Coquelin
2016-10-28 6:05 ` Xu, Qian Q
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