Re: [vpp-dev] Can "use mq eventfd" solve epoll wait h =?utf-8?Q?igh_cpu_usage_problem??=

Thu, 31 Oct 2019 19:58:50 -0700

Do you mean, if just use eventfds only, then I needn't set timeout  to 0 in ldp_epoll_pwait?
If so, then how to process unhandled_evts_vector in vppcom_epoll_wait timely? What I'm saying is,  another thread add event to unhandled_evts_vector during epoll_wait, or unhandled_evts_vector not process completely because of reaching maxevents.

Regards,
Hanlin
On 10/31/2019 23:34，Florin Coras<fcoras.li...@gmail.com> wrote：
Hi, 

use_mq_eventfd will help with vcl but as you’ve noticed it won’t help for ldp because there we need to poll both vcl and linux fds. Because mutex-condvar notifications can’t be epolled we have to constantly switch between linux and vcl epolled fds. One option going forward would be to change ldp to detect if vcl is using mutex-condvars or eventfds and in case of the latter poll linux fds and the mq’s eventfd in a linux epoll. 

Regards,
Florin

On Oct 31, 2019, at 5:54 AM, wanghanlin <wanghan...@corp.netease.com> wrote:

hi ALL，
I found app using VCL "epoll_wait" still occupy 70% cpu with "use_mq_eventfd" configuration even if very little traffic.
Then I investigate code in ldp_epoll_pwait, vls_epoll_wait is called with timeout equal to 0.
Then I have two questions:
1. What problems can "use_mq_eventfd" solve?
2.Any other way to decrease cpu usage?
Thanks!

code in  ldp_epoll_pwait:
do
    {
      if (!ldpw->epoll_wait_vcl)
{
  rv = vls_epoll_wait (ep_vlsh, events, maxevents, 0);
  if (rv > 0)
    {
      ldpw->epoll_wait_vcl = 1;
      goto done;
    }
  else if (rv < 0)
    {
      errno = -rv;
      rv = -1;
      goto done;
    }
}
      else
ldpw->epoll_wait_vcl = 0;

      if (libc_epfd > 0)
{
  rv = libc_epoll_pwait (libc_epfd, events, maxevents, 0, sigmask);
  if (rv != 0)
    goto done;
}
    }
  while ((timeout == -1) || (clib_time_now (&ldpw->clib_time) < max_time));
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