Re: io_uring networking performance degradation

[Michael Stoler <michaels@reduxio.com>]

Because of unstable working of perf over AWS VM I recheck test on
physical machine: Ubuntu 20.04, 5.8.0-50-generic kernel, CPU AMD EPYC
7272 12-Core Processor 3200MHz, BogoMIPS 5789.39, NIC melanox 5,
Speed: 25000Mb/s Full Duplex.
Over physical machine performance degradation is much less pronounced
but still exists:
io_uring-echo-server    Speed: 143081 request/sec, 143081 response/sec
epoll-echo-server   Speed: 150692 request/sec, 150692 response/sec
epoll-echo-server is 5% faster

"perf top" with io_uring-echo-server:
PerfTop:   16481 irqs/sec  kernel:98.5%  exact: 99.8% lost: 0/0 drop:
0/0 [4000Hz cycles],  (all, 24 CPUs)
-------------------------------------------------------------------------------
     8.66%  [kernel]          [k] __x86_indirect_thunk_rax
     8.49%  [kernel]          [k] copy_user_generic_string
     5.57%  [kernel]          [k] memset
     2.81%  [kernel]          [k] tcp_rate_skb_sent
     2.32%  [kernel]          [k] __alloc_skb
     2.16%  [kernel]          [k] __check_object_size
     1.44%  [unknown]         [k] 0xffffffffc100c296
     1.28%  [kernel]          [k] tcp_write_xmit
     1.22%  [kernel]          [k] iommu_dma_map_page
     1.16%  [kernel]          [k] kmem_cache_free
     1.14%  [kernel]          [k] __softirqentry_text_start
     1.06%  [unknown]         [k] 0xffffffffc1008a7e
     1.03%  [kernel]          [k] __skb_datagram_iter
     0.97%  [kernel]          [k] __dev_queue_xmit
     0.86%  [kernel]          [k] ipv4_mtu
     0.85%  [kernel]          [k] tcp_schedule_loss_probe
     0.80%  [kernel]          [k] tcp_release_cb
     0.78%  [unknown]         [k] 0xffffffffc100c290
     0.77%  [unknown]         [k] 0xffffffffc100c295
     0.76%  perf              [.] __symbols__insert

"perf top" with epoll-echo-server:
PerfTop:   24255 irqs/sec  kernel:98.3%  exact: 99.6% lost: 0/0 drop:
0/0 [4000Hz cycles],  (all, 24 CPUs)
-------------------------------------------------------------------------------
     8.77%  [kernel]          [k] __x86_indirect_thunk_rax
     7.50%  [kernel]          [k] copy_user_generic_string
     4.10%  [kernel]          [k] memset
     2.70%  [kernel]          [k] tcp_rate_skb_sent
     2.18%  [kernel]          [k] __check_object_size
     2.09%  [kernel]          [k] __alloc_skb
     1.61%  [unknown]         [k] 0xffffffffc100c296
     1.47%  [kernel]          [k] __virt_addr_valid
     1.40%  [kernel]          [k] iommu_dma_map_page
     1.37%  [unknown]         [k] 0xffffffffc1008a7e
     1.22%  [kernel]          [k] tcp_poll
     1.16%  [kernel]          [k] __softirqentry_text_start
     1.15%  [kernel]          [k] tcp_stream_memory_free
     1.07%  [kernel]          [k] tcp_write_xmit
     1.06%  [kernel]          [k] kmem_cache_free
     1.03%  [kernel]          [k] tcp_release_cb
     0.96%  [kernel]          [k] syscall_return_via_sysret
     0.90%  [kernel]          [k] __lock_text_start
     0.82%  [kernel]          [k] __copy_skb_header
     0.81%  [kernel]          [k] amd_iommu_map

Regards
    Michael Stoler

On Tue, Apr 20, 2021 at 1:44 PM Michael Stoler <michaels@reduxio.com> wrote:
>
> Hi, perf data and tops for linux-5.8 are here:
> http://rdxdownloads.rdxdyn.com/michael_stoler_perf_data.tgz
>
> Regards
>     Michael Stoler
>
> On Mon, Apr 19, 2021 at 5:27 PM Michael Stoler <michaels@reduxio.com> wrote:
> >
> > 1)  linux-5.12-rc8 shows generally same picture:
> >
> > average load, 70-85% CPU core usage, 128 bytes packets
> >     echo_bench --address '172.22.150.170:7777' --number 10 --duration
> > 60 --length 128`
> > epoll-echo-server:      Speed: 71513 request/sec, 71513 response/sec
> > io_uring_echo_server:   Speed: 64091 request/sec, 64091 response/sec
> >     epoll-echo-server is 11% faster
> >
> > high load, 95-100% CPU core usage, 128 bytes packets
> >     echo_bench --address '172.22.150.170:7777' --number 20 --duration
> > 60 --length 128`
> > epoll-echo-server:      Speed: 130186 request/sec, 130186 response/sec
> > io_uring_echo_server:   Speed: 109793 request/sec, 109793 response/sec
> >     epoll-echo-server is 18% faster
> >
> > average load, 70-85% CPU core usage, 2048 bytes packets
> >     echo_bench --address '172.22.150.170:7777' --number 10 --duration
> > 60 --length 2048`
> > epoll-echo-server:      Speed: 63082 request/sec, 63082 response/sec
> > io_uring_echo_server:   Speed: 59449 request/sec, 59449 response/sec
> >     epoll-echo-server is 6% faster
> >
> > high load, 95-100% CPU core usage, 2048 bytes packets
> >     echo_bench --address '172.22.150.170:7777' --number 20 --duration
> > 60 --length 2048`
> > epoll-echo-server:      Speed: 110402 request/sec, 110402 response/sec
> > io_uring_echo_server:   Speed: 88718 request/sec, 88718 response/sec
> >     epoll-echo-server is 24% faster
> >
> >
> > 2-3) The "perf top" doesn't work stable with Ubuntu over AWS. All the
> > time it shows errors: "Uhhuh. NMI received for unknown reason", "Do
> > you have a strange power saving mode enabled?",  "Dazed and confused,
> > but trying to continue".
> >
> > Regards
> >     Michael Stoler
> >
> > On Mon, Apr 19, 2021 at 1:20 PM Pavel Begunkov <asml.silence@gmail.com> wrote:
> > >
> > > On 4/19/21 10:13 AM, Michael Stoler wrote:
> > > > We are trying to reproduce reported on page
> > > > https://github.com/frevib/io_uring-echo-server/blob/master/benchmarks/benchmarks.md
> > > > results with a more realistic environment:
> > > > 1. Internode networking in AWS cluster with i3.16xlarge nodes type(25
> > > > Gigabit network connection between client and server)
> > > > 2. 128 and 2048 packet sizes, to simulate typical payloads
> > > > 3. 10 clients to get 75-95% CPU utilization by server to simulate
> > > > server's normal load
> > > > 4. 20 clients to get 100% CPU utilization by server to simulate
> > > > server's hard load
> > > >
> > > > Software:
> > > > 1. OS: Ubuntu 20.04.2 LTS HWE with 5.8.0-45-generic kernel with latest liburing
> > > > 2. io_uring-echo-server: https://github.com/frevib/io_uring-echo-server
> > > > 3. epoll-echo-server: https://github.com/frevib/epoll-echo-server
> > > > 4. benchmark: https://github.com/haraldh/rust_echo_bench
> > > > 5. all commands runs with "hwloc-bind os=eth1"
> > > >
> > > > The results are confusing, epoll_echo_server shows stable advantage
> > > > over io_uring-echo-server, despite reported advantage of
> > > > io_uring-echo-server:
> > > >
> > > > 128 bytes packet size, 10 clients, 75-95% CPU core utilization by server:
> > > > echo_bench --address '172.22.117.67:7777' -c 10 -t 60 -l 128
> > > > epoll_echo_server:      Speed: 80999 request/sec, 80999 response/sec
> > > > io_uring_echo_server:   Speed: 74488 request/sec, 74488 response/sec
> > > > epoll_echo_server is 8% faster
> > > >
> > > > 128 bytes packet size, 20 clients, 100% CPU core utilization by server:
> > > > echo_bench --address '172.22.117.67:7777' -c 20 -t 60 -l 128
> > > > epoll_echo_server:      Speed: 129063 request/sec, 129063 response/sec
> > > > io_uring_echo_server:    Speed: 102681 request/sec, 102681 response/sec
> > > > epoll_echo_server is 25% faster
> > > >
> > > > 2048 bytes packet size, 10 clients, 75-95% CPU core utilization by server:
> > > > echo_bench --address '172.22.117.67:7777' -c 10 -t 60 -l 2048
> > > > epoll_echo_server:       Speed: 74421 request/sec, 74421 response/sec
> > > > io_uring_echo_server:    Speed: 66510 request/sec, 66510 response/sec
> > > > epoll_echo_server is 11% faster
> > > >
> > > > 2048 bytes packet size, 20 clients, 100% CPU core utilization by server:
> > > > echo_bench --address '172.22.117.67:7777' -c 20 -t 60 -l 2048
> > > > epoll_echo_server:       Speed: 108704 request/sec, 108704 response/sec
> > > > io_uring_echo_server:    Speed: 85536 request/sec, 85536 response/sec
> > > > epoll_echo_server is 27% faster
> > > >
> > > > Why io_uring shows consistent performance degradation? What is going wrong?
> > >
> > > 5.8 is pretty old, and I'm not sure all the performance problems were
> > > addressed there. Apart from missing common optimisations as you may
> > > have seen in the thread, it looks to me it doesn't have sighd(?) lock
> > > hammering fix. Jens, knows better it has been backported or not.
> > >
> > > So, things you can do:
> > > 1) try out 5.12
> > > 2) attach `perf top` output or some other profiling for your 5.8
> > > 3) to have a more complete picture do 2) with 5.12
> > >
> > > Let's find what's gone wrong
> > >
> > > --
> > > Pavel Begunkov
> >
> >
> >
> > --
> > Michael Stoler
>
>
>
> --
> Michael Stoler



-- 
Michael Stoler