[erlang-questions] Improve performance of IO bounded server written in Erlang via having pollset for each scheduler and bind port to scheduler together with process

erlang <>
Tue Jul 10 23:14:54 CEST 2012


Hi, all (first time)
on start - i'm sorry for my englisch language.
i think that the problem is on all lines where you use "io:format"
In my system when i start wrote in erlang I used many times io:format 
for debug. It wos big bottleneck.


JanM


W dniu 2012-07-09 11:01, Wei Cao pisze:
> Hi, all
>
> We wrote a proxy server in Erlang, the proxy's logic is rather simple,
> it listens on some TCP port, establishes new connection from user
> client, forward packets back and forth between the client and backend
> server after authentication until connection is closed.
>
> It's very easy to write such a proxy in Erlang, fork a process for
> each new user connection and connect to the backend server in the same
> process,  the process works like a pipe, sockets from both side is set
> to the active once mode, whenever a tcp packet is received from one
> socket, the packet will be sent to other socket. (A simplified version
> of proxy code is attached at the end of the mail)
>
> However, the performance is not quite satisfying, the proxy can handle
> maximum only 40k requests on our 16 core machine(Intel Xeon L5630,
> 2.13GHz) with heavy stress(100 concurrent clients). We then analyzed
> the behavior of beam.smp use tools like tcprstat, mpstat, perf, and
> SystemTap.
>
> tcprstat shows QPS is about 40k, have average 1.7 millisecond latency
> for each request.
>
> timestamp	count	max	min	avg	med	stddev	95_max	95_avg	95_std	99_max	99_avg	99_std
> 1341813326	39416	17873	953	1718	1519	724	2919	1609	340	3813	1674	462
> 1341813327	40528	9275	884	1645	1493	491	2777	1559	290	3508	1619	409
> 1341813328	40009	18105	925	1694	1507	714	2868	1586	328	3753	1650	450
>
>
> mpstat shows 30% CPU is idle,
>
> 03:30:19 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft
> %steal  %guest   %idle
> 03:30:20 PM  all   38.69    0.00   21.92    0.00    0.06    7.52
> 0.00    0.00   31.80
> 03:30:21 PM  all   37.56    0.00   21.99    0.00    0.00    7.50
> 0.00    0.00   32.95
>
> and perf top shows, much time is wasted in scheduler_wait, in spin wait I guess.
>
> 9320.00 19.8% scheduler_wait
> /home/mingsong.cw/erlangr16b/lib/erlang/erts-5.10/bin/beam.smp
> 1813.00  3.9% process_main
> /home/mingsong.cw/erlangr16b/lib/erlang/erts-5.10/bin/beam.smp
> 1379.00  2.9% _spin_lock
> /usr/lib/debug/lib/modules/2.6.32-131.21.1.tb477.el6.x86_64/vmlinux
> 1201.00  2.6% schedule
> /home/mingsong.cw/erlangr16b/lib/erlang/erts-5.10/bin/beam.smp
>
> It seems the performance may be associated with scheduler_wait() and
> erts_check_io(), with a SystemTap script(attached at the end of this
> mail), we can find out how many times the system call epoll_wait is
> invoked by beam.smp and each time, how many revents it gets.
>
>   cpu                                       process      times
> revents        min        max        avg   timeouts
>   all
> 1754     128042          -          -         73          3
> [14]                                      beam.smp        151
> 14127         82         97         93          0
> [ 5]                                      beam.smp        142
> 13291         83         97         93          0
> [13]                                      beam.smp        127
> 11948         86         96         94          0
> [ 6]                                      beam.smp        127
> 11836         81         96         93          0
> [ 4]                                      beam.smp        121
> 11323         81         96         93          0
> [15]                                      beam.smp        117
> 10935         83         96         93          0
> [12]                                      beam.smp        486
> 10128          0         96         20          2
> [ 1]                                      beam.smp         71
> 6549         71        100         92          0
> [ 2]                                      beam.smp         62
> 5695         82         96         91          0
> [ 7]                                      beam.smp         55
> 5102         81         95         92          0
> [11]                                      beam.smp         52
> 4822         85         95         92          0
> [ 9]                                      beam.smp         52
> 4799         85         95         92          0
> [ 8]                                      beam.smp         51
> 4680         78         95         91          0
> [10]                                      beam.smp         49
> 4508         85         97         92          0
> [ 3]                                      beam.smp         46
> 4211         81         95         91          0
> [ 0]                                      beam.smp         44
> 4088         83         95         92          0
>
> The resuls shows, epoll_wait is invoked 1754 times each second, and
> get 73 io events in average. This is unacceptable for writing high
> performance server. Because if epoll_wait is invoked no more than 2k
> times per second, then read/write a packet would cost more than 500ms,
> which causes long delay and affects the throughput finally.
>
> The problem relies on there is only one global pollset in system wide,
> so at a time there is no more than one scheduler can call
> erts_check_io() to obtain pending io tasks from underlying pollset,
> and no scheduler can call erts_check_io() before all pending io
> tasks're processed, so for IO bounded application, it's very likely
> that a scheduler finish its own job, but must wait idly for other
> schedulers to complete theirs.
>
> Hence, we develops a patch to slove this problem, by having a pollset
> for each scheduler, so that each scheduler can invoke erts_check_io()
> on its own pollset concurrently. After a scheduler complete its tasks,
> it can invoke erts_check_io() immediately no matter what state other
> schedulers're in. This patch also handles port migration situation,
> all used file descriptors in each port're recorded, when a port is
> migrated, these
> fd 're removed from original scheduler's pollset, and added to new scheduler's.
>
> Bind port to scheduler together with process is also helpful to
> performance, it reduces the cost of thread switches and
> synchronization, and bound port won't be migrated between schedulers.
>
> After apply the two patches, with the same pressure(100 concurrent
> clients),epoll_wait is invoked 49332  times per second, and get 3
> revents each time in average, that is to say, our server responds
> quicker and become more realtime.
>
>   cpu                                       process      times
> revents        min        max        avg   timeouts
>   all
> 49332     217186          -          -          4          3
> [ 2]                                      beam.smp       3219
> 16050          2          7          4          0
> [11]                                      beam.smp       4275
> 16033          1          6          3          0
> [ 8]                                      beam.smp       4240
> 15992          1          6          3          0
> [ 9]                                      beam.smp       4316
> 15964          0          6          3          2
> [10]                                      beam.smp       4139
> 15851          1          6          3          0
> [ 3]                                      beam.smp       4256
> 15816          1          6          3          0
> [ 1]                                      beam.smp       3107
> 15800          2          7          5          0
> [ 0]                                      beam.smp       3727
> 15259          1          6          4          0
> [ 7]                                      beam.smp       2810
> 14722          3          7          5          0
> [13]                                      beam.smp       1981
> 11499          4          7          5          0
> [15]                                      beam.smp       2285
> 10942          3          6          4          0
> [14]                                      beam.smp       2258
> 10866          3          6          4          0
> [ 4]                                      beam.smp       2246
> 10849          3          6          4          0
> [ 6]                                      beam.smp       2206
> 10730          3          6          4          0
> [12]                                      beam.smp       2173
> 10573          3          6          4          0
> [ 5]                                      beam.smp       2093
> 10240          3          6          4          0
>
> scheduler_wait no longer take so much time now,
>
>                169.00  6.2% process_main                    beam.smp
>                 55.00  2.0% _spin_lock                      [kernel]
>                 45.00  1.7% driver_deliver_term             beam.smp
>
> so is idle CPU time
> 04:30:44 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft
> %steal  %guest   %idle
> 04:30:45 PM  all   60.34    0.00   21.44    0.00    0.06   16.45
> 0.00    0.00    1.71
> 04:30:46 PM  all   60.99    0.00   21.22    0.00    0.00   16.26
> 0.00    0.00    1.52
>
> and tcprstat shows, QPS is getting 100K, latency is less than 1 millisecond
>
> timestamp	count	max	min	avg	med	stddev	95_max	95_avg	95_std	99_max	99_avg	99_std
> 1341822689	96078	11592	314	910	817	311	1447	869	228	1777	897	263
> 1341822690	100651	24245	209	914	819	381	1458	870	229	1800	899	263
>
> I also write a extreamly simple keep-alive http server(attached at the
> end of mail), to compare performance before and after applying the
> patches, mearused with apache ab tool(ab -n 1000000 -c 100 -k ), a 30%
> performance gain can be get.
>
> before
> Requests per second:    103671.70 [#/sec] (mean)
> Time per request:       0.965 [ms] (mean)
>
> after
> Requests per second:    133701.24 [#/sec] (mean)
> Time per request:       0.748 [ms] (mean)
>
> Patches can be found at github, compile with
> ./configure CFLAGS=-DERTS_POLLSET_PER_SCHEDULER
>
> Pollset per scheduler:
>
> git fetch git://github.com/weicao/otp.git pollset_per_scheduler
>
> https://github.com/weicao/otp/compare/weicao:master...weicao:pollset_per_scheduler
> https://github.com/weicao/otp/compare/weicao:master...weicao:pollset_per_scheduler.patch
>
>
> Bind port to scheduler:
>
> git fetch git://github.com/weicao/otp.git bind_port_to_scheduler
>
> https://github.com/weicao/otp/compare/weicao:pollset_per_scheduler...weicao:bind_port_to_scheduler
> https://github.com/weicao/otp/compare/weicao:pollset_per_scheduler...weicao:bind_port_to_scheduler.patch
>
>
> Appendix:
>
> -----------------------------------
> proxy.erl
> ------------------------------------
>
> -module(proxy).
> -compile(export_all).
>
> -define(RECBUF_SIZE, 8192).
> -define(ACCEPT_TIMEOUT, 2000).
>
> start([MyPortAtom, DestIpAtom, DestPortAtom]) ->
>      {MyPort, []} =  string:to_integer(atom_to_list(MyPortAtom)),
>      DestIp = atom_to_list(DestIpAtom),
>      {DestPort, []} = string:to_integer(atom_to_list(DestPortAtom)),
>      listen(MyPort, DestIp, DestPort),
>      receive Any ->
>          io:format("recv ~p~n", [Any])
>      end.
>
> listen(MyPort, DestIp, DestPort) ->
>      io:format("start proxy on [local] 0.0.0.0:~p -> [remote] ~p:~p~n",
> [MyPort, DestIp, DestPort]),
>      case gen_tcp:listen(MyPort,
>             [inet,
>              {ip, {0,0,0,0}},
>              binary,
>              {reuseaddr, true},
>              {recbuf, ?RECBUF_SIZE},
>              {active, false},
>              {nodelay, true}
>             ]) of
>          {ok, Listen} ->
>              N = erlang:system_info(schedulers),
>              lists:foreach(fun(I) -> accept(Listen, DestIp, DestPort,
> I) end, lists:seq(1,N));
>          {error, Reason} ->
>              io:format("error listen ~p~n", [Reason])
>      end.
>
> accept(Listen, DestIp, DestPort, I) ->
>      spawn_opt(?MODULE, loop, [Listen, DestIp, DestPort, I], [{scheduler, I}]).
>
> loop(Listen, DestIp, DestPort, I) ->
>      case gen_tcp:accept(Listen, ?ACCEPT_TIMEOUT) of
>          {ok, S1} ->
>              accept(Listen, DestIp, DestPort, I),
>              case catch gen_tcp:connect(DestIp, DestPort,
>                             [inet, binary, {active, false},
>                              {reuseaddr, true}, {nodelay, true}]) of
>                  {ok, S2} ->
>                      io:format("new connection~n"),
>                      loop1(S1, S2);
>                  {error, Reason} ->
>                      io:format("error connect ~p~n", [Reason])
>              end;
>          {error, timeout} ->
>              loop(Listen, DestIp, DestPort, I);
>          Error ->
>              io:format("error accept ~p~n", [Error]),
>              accept(Listen, DestIp, DestPort, I)
>      end.
>
> loop1(S1, S2) ->
>      active(S1, S2),
>      receive
>          {tcp, S1, Data} ->
>              gen_tcp:send(S2, Data),
>              loop1(S1, S2);
>          {tcp, S2, Data} ->
>              gen_tcp:send(S1, Data),
>              loop1(S1, S2);
>          {tcp_closed, S1} ->
>              io:format("S1 close~n"),
>              gen_tcp:close(S1),
>              gen_tcp:close(S2);
>          {tcp_closed, S2} ->
>              io:format("S2 close~n"),
>              gen_tcp:close(S1),
>              gen_tcp:close(S2)
>      end.
>
> active(S1,S2)->
>      inet:setopts(S1, [{active, once}]),
>      inet:setopts(S2, [{active, once}]).
>
> -----------------------------------
> epollwait.stp
> ------------------------------------
> #! /usr/bin/env stap
> #
> #
>
> global epoll_timeout_flag, epoll_count, epoll_min, epoll_max,
> epoll_times, epoll_timeouts
>
> probe  syscall.epoll_wait {
>      if(timeout > 0) {
>          epoll_timeout_flag[pid()] = 1
>      }
> }
>
> probe  syscall.epoll_wait.return {
>    c = cpu()
>    p = execname()
>
>    epoll_times[c,p] ++
>    epoll_count[c,p] += $return
>
>    if($return == 0 && pid() in epoll_timeout_flag) {
>      epoll_timeouts[c,p] ++
>      delete epoll_timeout_flag[pid()]
>    }
>
>    if(!([c, p] in epoll_min)) {
>      epoll_min[c,p] = $return
>    } else if($return < epoll_min[c,p]) {
>      epoll_min[c,p] = $return
>    }
>
>
>    if($return > epoll_max[c,p]) {
>      epoll_max[c,p] = $return
>    }
> }
>
> probe timer.s($1) {
>    printf ("%4s %45s %10s %10s %10s %10s %10s %10s\n", "cpu",
> "process", "times", "revents", "min", "max", "avg", "timeouts" )
>    foreach ([cpu, process] in epoll_count- limit 20) {
>        all_epoll_times += epoll_times[cpu,process]
>        all_epoll_count += epoll_count[cpu,process]
>        all_epoll_timeouts += epoll_timeouts[cpu,process]
>    }
>    printf ("%4s %45s %10d %10d %10s %10s %10d %10d\n",
>      "all", "", all_epoll_times, all_epoll_count, "-", "-",
>      all_epoll_count == 0? 0:all_epoll_count/all_epoll_times, all_epoll_timeouts)
>
>    foreach ([cpu, process] in epoll_count- limit 20) {
>       printf ("[%2d] %45s %10d %10d %10d %10d %10d %10d\n",
>          cpu, process, epoll_times[cpu, process], epoll_count[cpu, process],
>          epoll_min[cpu, process], epoll_max[cpu, process],
>          epoll_count[cpu,process]/epoll_times[cpu,process],
>          epoll_timeouts[cpu,process])
>    }
>    delete epoll_count
>    delete epoll_min
>    delete epoll_max
>    delete epoll_times
>    delete epoll_timeouts
>    printf ("--------------------------------------------------------------------------\n\n"
> )
> }
>
> ------------------------------------------------
> ehttpd.erl
> -------------------------------------------------
> -module(ehttpd).
> -compile(export_all).
>
> start() ->
>      start(8888).
> start(Port) ->
>      N = erlang:system_info(schedulers),
>      listen(Port, N),
>      io:format("ehttpd ready with ~b schedulers on port ~b~n", [N, Port]),
>
>      register(?MODULE, self()),
>      receive Any -> io:format("~p~n", [Any]) end.  %% to stop: ehttpd!stop.
>
> listen(Port, N) ->
>      Opts = [inet,
>              binary,
>              {active, false},
>              {recbuf, 8192},
>              {nodelay,true},
>              {reuseaddr, true}],
>
>      {ok, S} = gen_tcp:listen(Port, Opts),
>      lists:foreach(fun(I)-> spawn_opt(?MODULE, accept, [S, I],
> [{scheduler, I}]) end, lists:seq(1, N)).
>
> accept(S, I) ->
>      case gen_tcp:accept(S) of
>          {ok, Socket} ->
>              spawn_opt(?MODULE, accept, [S, I],[{scheduler,I}] ),
>              io:format("new connection @~p~n", [I]),
>              loop(Socket,<<>>);
>          Error    -> erlang:error(Error)
>      end.
>
> loop(S,B) ->
>      inet:setopts(S, [{active, once}]),
>      receive
>          {tcp, S, Data} ->
>              B1 = <<B/binary, Data/binary>>,
>              case binary:part(B1,{byte_size(B1), -4}) of
>                  <<"\r\n\r\n">> ->
>                      Response = <<"HTTP/1.1 200 OK\r\nContent-Length:
> 12\r\nConnection: Keep-Alive\r\n\r\nhello world!">>,
>                      gen_tcp:send(S, Response),
>                      loop(S, <<>>);
>                  _ ->
>                      loop(S, B1)
>              end;
>          {tcp_closed, S} ->
>              io:format("connection closed forced~n"),
>              gen_tcp:close(S);
>          Error ->
>              io:format("unexpected message~p~n", [Error]),
>              Error
>      end.
>
>





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