[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

Zabrane Mickael <>
Wed Jul 11 02:24:53 CEST 2012


Hi Wei,

I did some other tests on our 8-Cores 64-bit machine:

before: 157141 rps
after: 80245 rps

Same behaviour as before ... hope this help.

Regards,
Zabrane

On Jul 10, 2012, at 4:30 AM, Wei Cao wrote:

> My tests were all keepalived/persistent connections, and there was
> significant performance gain in these situations. but I wrote a http
> server with short connection just now, the performance did drop down,
> I'll find it out later :).
> 
> 2012/7/10 Zabrane Mickael <>:
>> Hi,
>> 
>> Performance of our HTTP Web Server drops down after applying your patches.
>> 
>> Box: Linux F17, 4GB of RAM:
>> $ lscpu
>> Architecture:          i686
>> CPU op-mode(s):        32-bit, 64-bit
>> Byte Order:            Little Endian
>> CPU(s):                4
>> On-line CPU(s) list:   0-3
>> Thread(s) per core:    1
>> Core(s) per socket:    4
>> Socket(s):             1
>> Vendor ID:             GenuineIntel
>> CPU family:            6
>> Model:                 23
>> Stepping:              7
>> CPU MHz:               2499.772
>> BogoMIPS:              4999.54
>> Virtualization:        VT-x
>> L1d cache:             32K
>> L1i cache:             32K
>> L2 cache:              3072K
>> 
>> Bench:
>> before: 77787 rps
>> after:    53056 rps
>> 
>> Any hint to explain this result Wei ?
>> 
>> Regards,
>> Zabrane
>> 
>> 
>> On Jul 9, 2012, at 11:01 AM, Wei Cao wrote:
>> 
>> 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.
>> 
>> 
>> --
>> 
>> Best,
>> 
>> Wei Cao
>> _______________________________________________
>> erlang-questions mailing list
>> 
>> http://erlang.org/mailman/listinfo/erlang-questions
>> 
>> 
>> 
> 
> 
> 
> -- 
> 
> Best,
> 
> Wei Cao






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