[zeromq-dev] performance issue in zmq_proxy_steerable()

[Bill Torpey]

HI Claudio:

You might want to try a later version — there was a performance regression on certain platforms that is documented here: https://github.com/zeromq/libzmq/issues/3373 <https://github.com/zeromq/libzmq/issues/3373> and was resolved by a commit by Doron (5ecf8f9) subsequent to release of 4.3.1.  

Hope this helps.

Bill


> On Mar 1, 2019, at 11:44 AM, 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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