Re: [PATCH RFC v8 02/11] vhost: use batched get_vq_desc version

[Eugenio Perez Martin <eperezma@redhat.com>]

On Wed, Jul 1, 2020 at 4:10 PM Jason Wang <jasowang@redhat.com> wrote:
>
>
> On 2020/7/1 下午9:04, Eugenio Perez Martin wrote:
> > On Wed, Jul 1, 2020 at 2:40 PM Jason Wang <jasowang@redhat.com> wrote:
> >>
> >> On 2020/7/1 下午6:43, Eugenio Perez Martin wrote:
> >>> On Tue, Jun 23, 2020 at 6:15 PM Eugenio Perez Martin
> >>> <eperezma@redhat.com> wrote:
> >>>> On Mon, Jun 22, 2020 at 6:29 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >>>>> On Mon, Jun 22, 2020 at 06:11:21PM +0200, Eugenio Perez Martin wrote:
> >>>>>> On Mon, Jun 22, 2020 at 5:55 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >>>>>>> On Fri, Jun 19, 2020 at 08:07:57PM +0200, Eugenio Perez Martin wrote:
> >>>>>>>> On Mon, Jun 15, 2020 at 2:28 PM Eugenio Perez Martin
> >>>>>>>> <eperezma@redhat.com> wrote:
> >>>>>>>>> On Thu, Jun 11, 2020 at 5:22 PM Konrad Rzeszutek Wilk
> >>>>>>>>> <konrad.wilk@oracle.com> wrote:
> >>>>>>>>>> On Thu, Jun 11, 2020 at 07:34:19AM -0400, Michael S. Tsirkin wrote:
> >>>>>>>>>>> As testing shows no performance change, switch to that now.
> >>>>>>>>>> What kind of testing? 100GiB? Low latency?
> >>>>>>>>>>
> >>>>>>>>> Hi Konrad.
> >>>>>>>>>
> >>>>>>>>> I tested this version of the patch:
> >>>>>>>>> https://lkml.org/lkml/2019/10/13/42
> >>>>>>>>>
> >>>>>>>>> It was tested for throughput with DPDK's testpmd (as described in
> >>>>>>>>> http://doc.dpdk.org/guides/howto/virtio_user_as_exceptional_path.html)
> >>>>>>>>> and kernel pktgen. No latency tests were performed by me. Maybe it is
> >>>>>>>>> interesting to perform a latency test or just a different set of tests
> >>>>>>>>> over a recent version.
> >>>>>>>>>
> >>>>>>>>> Thanks!
> >>>>>>>> I have repeated the tests with v9, and results are a little bit different:
> >>>>>>>> * If I test opening it with testpmd, I see no change between versions
> >>>>>>> OK that is testpmd on guest, right? And vhost-net on the host?
> >>>>>>>
> >>>>>> Hi Michael.
> >>>>>>
> >>>>>> No, sorry, as described in
> >>>>>> http://doc.dpdk.org/guides/howto/virtio_user_as_exceptional_path.html.
> >>>>>> But I could add to test it in the guest too.
> >>>>>>
> >>>>>> These kinds of raw packets "bursts" do not show performance
> >>>>>> differences, but I could test deeper if you think it would be worth
> >>>>>> it.
> >>>>> Oh ok, so this is without guest, with virtio-user.
> >>>>> It might be worth checking dpdk within guest too just
> >>>>> as another data point.
> >>>>>
> >>>> Ok, I will do it!
> >>>>
> >>>>>>>> * If I forward packets between two vhost-net interfaces in the guest
> >>>>>>>> using a linux bridge in the host:
> >>>>>>> And here I guess you mean virtio-net in the guest kernel?
> >>>>>> Yes, sorry: Two virtio-net interfaces connected with a linux bridge in
> >>>>>> the host. More precisely:
> >>>>>> * Adding one of the interfaces to another namespace, assigning it an
> >>>>>> IP, and starting netserver there.
> >>>>>> * Assign another IP in the range manually to the other virtual net
> >>>>>> interface, and start the desired test there.
> >>>>>>
> >>>>>> If you think it would be better to perform then differently please let me know.
> >>>>> Not sure why you bother with namespaces since you said you are
> >>>>> using L2 bridging. I guess it's unimportant.
> >>>>>
> >>>> Sorry, I think I should have provided more context about that.
> >>>>
> >>>> The only reason to use namespaces is to force the traffic of these
> >>>> netperf tests to go through the external bridge. To test netperf
> >>>> different possibilities than the testpmd (or pktgen or others "blast
> >>>> of frames unconditionally" tests).
> >>>>
> >>>> This way, I make sure that is the same version of everything in the
> >>>> guest, and is a little bit easier to manage cpu affinity, start and
> >>>> stop testing...
> >>>>
> >>>> I could use a different VM for sending and receiving, but I find this
> >>>> way a faster one and it should not introduce a lot of noise. I can
> >>>> test with two VM if you think that this use of network namespace
> >>>> introduces too much noise.
> >>>>
> >>>> Thanks!
> >>>>
> >>>>>>>>     - netperf UDP_STREAM shows a performance increase of 1.8, almost
> >>>>>>>> doubling performance. This gets lower as frame size increase.
> >>> Regarding UDP_STREAM:
> >>> * with event_idx=on: The performance difference is reduced a lot if
> >>> applied affinity properly (manually assigning CPU on host/guest and
> >>> setting IRQs on guest), making them perform equally with and without
> >>> the patch again. Maybe the batching makes the scheduler perform
> >>> better.
> >>
> >> Note that for UDP_STREAM, the result is pretty trick to be analyzed. E.g
> >> setting a sndbuf for TAP may help for the performance (reduce the drop).
> >>
> > Ok, will add that to the test. Thanks!
>
>
> Actually, it's better to skip the UDP_STREAM test since:
>
> - My understanding is very few application is using raw UDP stream
> - It's hard to analyze (usually you need to count the drop ratio etc)
>
>
> >
> >>>>>>>>     - rests of the test goes noticeably worse: UDP_RR goes from ~6347
> >>>>>>>> transactions/sec to 5830
> >>> * Regarding UDP_RR, TCP_STREAM, and TCP_RR, proper CPU pinning makes
> >>> them perform similarly again, only a very small performance drop
> >>> observed. It could be just noise.
> >>> ** All of them perform better than vanilla if event_idx=off, not sure
> >>> why. I can try to repeat them if you suspect that can be a test
> >>> failure.
> >>>
> >>> * With testpmd and event_idx=off, if I send from the VM to host, I see
> >>> a performance increment especially in small packets. The buf api also
> >>> increases performance compared with only batching: Sending the minimum
> >>> packet size in testpmd makes pps go from 356kpps to 473 kpps.
> >>
> >> What's your setup for this. The number looks rather low. I'd expected
> >> 1-2 Mpps at least.
> >>
> > Intel(R) Xeon(R) CPU E5-2650 v4 @ 2.20GHz, 2 NUMA nodes of 16G memory
> > each, and no device assigned to the NUMA node I'm testing in. Too low
> > for testpmd AF_PACKET driver too?
>
>
> I don't test AF_PACKET, I guess it should use the V3 which mmap based
> zerocopy interface.
>
> And it might worth to check the cpu utilization of vhost thread. It's
> required to stress it as 100% otherwise there could be a bottleneck
> somewhere.
>
>
> >
> >>> Sending
> >>> 1024 length UDP-PDU makes it go from 570kpps to 64 kpps.
> >>>
> >>> Something strange I observe in these tests: I get more pps the bigger
> >>> the transmitted buffer size is. Not sure why.
> >>>
> >>> ** Sending from the host to the VM does not make a big change with the
> >>> patches in small packets scenario (minimum, 64 bytes, about 645
> >>> without the patch, ~625 with batch and batch+buf api). If the packets
> >>> are bigger, I can see a performance increase: with 256 bits,
> >>
> >> I think you meant bytes?
> >>
> > Yes, sorry.
> >
> >>>    it goes
> >>> from 590kpps to about 600kpps, and in case of 1500 bytes payload it
> >>> gets from 348kpps to 528kpps, so it is clearly an improvement.
> >>>
> >>> * with testpmd and event_idx=on, batching+buf api perform similarly in
> >>> both directions.
> >>>
> >>> All of testpmd tests were performed with no linux bridge, just a
> >>> host's tap interface (<interface type='ethernet'> in xml),
> >>
> >> What DPDK driver did you use in the test (AF_PACKET?).
> >>
> > Yes, both testpmd are using AF_PACKET driver.
>
>
> I see, using AF_PACKET means extra layers of issues need to be analyzed
> which is probably not good.
>
>
> >
> >>> with a
> >>> testpmd txonly and another in rxonly forward mode, and using the
> >>> receiving side packets/bytes data. Guest's rps, xps and interrupts,
> >>> and host's vhost threads affinity were also tuned in each test to
> >>> schedule both testpmd and vhost in different processors.
> >>
> >> My feeling is that if we start from simple setup, it would be more
> >> easier as a start. E.g start without an VM.
> >>
> >> 1) TX: testpmd(txonly) -> virtio-user -> vhost_net -> XDP_DROP on TAP
> >> 2) RX: pkgetn -> TAP -> vhost_net -> testpmd(rxonly)
> >>
> > Got it. Is there a reason to prefer pktgen over testpmd?
>
>
> I think the reason is using testpmd you must use a userspace kernel
> interface (AF_PACKET), and it could not be as fast as pktgen since:
>
> - it talks directly to xmit of TAP
> - skb can be cloned
>

Hi!

Here it is the result of the tests. Details on [1].

Tx:
===

For tx packets it seems that the batching patch makes things a little
bit worse, but the buf_api outperforms baseline by a 7%:

* We start with a baseline of 4208772.571 pps and 269361444.6 bytes/s [2].
* When we add the batching, I see a small performance decrease:
4133292.308 and 264530707.7 bytes/s.
* However, the buf api it outperform the baseline: 4551319.631pps,
291205178.1 bytes/s

I don't have numbers on the receiver side since it is just a XDP_DROP.
I think it would be interesting to see them.

Rx:
===

Regarding Rx, the reverse is observed: a small performance increase is
observed with batching (~2%), but buf_api makes tests perform equally
to baseline.

pktgen was called using pktgen_sample01_simple.sh, with the environment:
DEV="$tap_name" F_THREAD=1 DST_MAC=$MAC_ADDR COUNT=$((2500000*25))
SKB_CLONE=$((2**31))

And testpmd is the same as Tx but with forward-mode=rxonly.

Pktgen reports:
Baseline: 1853025pps 622Mb/sec (622616400bps) errors: 7915231
Batch: 1891404pps 635Mb/sec (635511744bps) errors: 4926093
Buf_api: 1844008pps 619Mb/sec (619586688bps) errors: 47766692

Testpmd reports:
Baseline: 1854448pps, 860464156 bps. [3]
Batch: 1892844.25pps, 878280070bps.
Buf_api: 1846139.75pps, 856609120bps.

Any thoughts?

Thanks!

[1]
Testpmd options: -l 1,3
--vdev=virtio_user0,mac=01:02:03:04:05:06,path=/dev/vhost-net,queue_size=1024
-- --auto-start --stats-period 5 --tx-offloads="$TX_OFFLOADS"
--rx-offloads="$RX_OFFLOADS" --txd=4096 --rxd=4096 --burst=512
--forward-mode=txonly

Where offloads were obtained manually running with
--[tr]x-offloads=0x8fff and examining testpmd response:
declare -r RX_OFFLOADS=0x81d
declare -r TX_OFFLOADS=0x802d

All of the tests results are an average of at least 3 samples of
testpmd, discarding the obvious deviations at start/end (like warming
up or waiting for pktgen to start). The result of pktgen is directly
c&p from its output.

The numbers do not change very much from one stats printing to another
of testpmd.

[2] Obtained subtracting each accumulated tx-packets from one stats
print to the previous one. If we attend testpmd output about Tx-pps,
it counts a little bit less performance, but it follows the same
pattern:

Testpmd pps/bps stats:
Baseline: 3510826.25 pps, 1797887912bps = 224735989bytes/sec
Batch: 3448515.571pps, 1765640226bps = 220705028.3bytes/sec
Buf api: 3794115.333pps, 1942587286bps = 242823410.8bytes/sec

[3] This is obtained using the rx-pps/rx-bps report of testpmd.

Seems strange to me that the relation between pps/bps is ~336 this
time, and between accumulated pkts/accumulated bytes is ~58. Also, the
relation between them is not even close to 8.

However, testpmd shows a lot of absolute packets received. If we see
the received packets in a period subtracting from the previous one,
testpmd tells that receive more pps than pktgen tx-pps:
Baseline: ~2222668.667pps 128914784.3bps.
Batch: 2269260.933pps, 131617134.9bps
Buf_api: 2213226.467pps, 128367135.9bp