[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
zabrane3@REDACTED
Tue Jul 10 01:14:33 CEST 2012
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
> erlang-questions@REDACTED
> http://erlang.org/mailman/listinfo/erlang-questions
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