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

[Jason Wang]

On 2020/7/10 äå1:37, Michael S. Tsirkin wrote:
> On Thu, Jul 09, 2020 at 06:46:13PM +0200, Eugenio Perez Martin wrote:
> > On Wed, Jul 1, 2020 at 4:10 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > > On 2020/7/1 äå9:04, Eugenio Perez Martin wrote:
> > > > On Wed, Jul 1, 2020 at 2:40 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > > > > On 2020/7/1 äå6:43, Eugenio Perez Martin wrote:
> > > > > > On Tue, Jun 23, 2020 at 6:15 PM Eugenio Perez Martin
> > > > > > <eperezma@xxxxxxxxxx> wrote:
> > > > > > > On Mon, Jun 22, 2020 at 6:29 PM Michael S. Tsirkin <mst@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx> wrote:
> > > > > > > > > > > > On Thu, Jun 11, 2020 at 5:22 PM Konrad Rzeszutek Wilk
> > > > > > > > > > > > <konrad.wilk@xxxxxxxxxx> 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
> How about playing with the batch size? Make it a mod parameter instead
> of the hard coded 64, and measure for all values 1 to 64 ...


Right, according to the test result, 64 seems to be too aggressive in 
the case of TX.

And it might also be worth to check:

1) Whether vhost thread is stressed as 100% CPU utilization, if not, 
there's bottleneck elsewhere
2) For RX test, make sure pktgen kthread is running in the same NUMA 
node with virtio-user

Thanks


>