[zeromq-dev] performance issue in zmq_proxy_steerable()

[Doron Somech]

You cannot throttle the getsockopt of ZMQ_EVENTS.
As you should only throttle from within recv & send.

My suggestion is, to write the proxy code by hand, the trick to get maximum
performance is to call zmq_recv with DONT_WAIT flag until you get EAGAIN.
So when the zmq_poll signal that a socket is ready for reading you read as
much as you can.
That way, you don't call the process_commands as often.


On Fri, Mar 1, 2019 at 6:46 PM Claudio U. <retmt at gmx.com> wrote:

> Hi all,
>
> I am facing a performance issue with a thread running
> zmq_proxy_steerable(), which subscribes to multiple inproc XPUB sockets and
> forwards data to a tcp XPUB socket.
> I am using ZMQ latest version 4.3.1
>
> I noticed a huge amount of calls to poll() that limit the throughput to
> ~120kpps. From strace output I see:
>
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
> 81.77    1.419731           4    371984           poll
> 18.22    0.316395           7     45533           write
>  0.01    0.000106           5        22           read
>  0.00    0.000015          15         1           restart_syscall
> ------ ----------- ----------- --------- --------- ----------------
> 100.00    1.736247                417540           total
>
>
> If I use gdb to stop on the poll() it seems that most of the time it is
> called by:
>
> zmq::socket_base_t::getsockopt(...)
>
> that calls process_command() with flag throttle_=false :
>
>   const int rc = process_commands (0, false); // socket_base.cpp:450
>   // prototype: int zmq::socket_base_t::process_commands (int timeout_,
> bool throttle_)
>
> I tried to change that line to throttle=true and to tune the parameters in
> config.hpp :
>   inbound_poll_rate = 100 -> inbound_poll_rate = 10000
>   max_command_delay = 3000000 -> max_command_delay  = 3000000000
>
>
> The result is an increase of the throughput from ~120kpps to ~230kpps due
> to the lower amount of calls to poll():
>
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
> 55.64    1.278789           4    295038           poll
> 44.35    1.019367           7    147408           write
>  0.00    0.000086           4        22           read
>  0.00    0.000057          10         6           futex
> ------ ----------- ----------- --------- --------- ----------------
> 100.00    2.298299                442474           total
>
> Is it safe to enable the throttle in getsockopt()?
> Is there any side effect beside a maybe longer response time to commands?
> In case it is safe, do you accept a PR to change throttle=true and make
> inbound_poll_rate and max_command_delay configurable?
>
>
> Regards,
> Claudio
>
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