Probably due to the vpp process sitting in an epoll_pwait(). See .../src/vlib/unix/input.c:linux_epoll_input_inline(...).
The tw_timer code does its best, but if you don’t call the tw_timer_expire_timers_XXX(...) method precisely it won’t yield the sort of precision you’re looking for. If you configure the timer wheel at 100ms granularity you should expect timers to pop within +-50 ms of when you expect them to pop, even if you call the tw_timer_expire_timers_XXX method precisely. The code picks the nearest slot, and if slots are 100ms wide, well, you get the idea. Dave From: vpp-dev@lists.fd.io <vpp-dev@lists.fd.io> On Behalf Of shaligra...@gmail.com Sent: Saturday, December 8, 2018 1:54 PM To: vpp-dev@lists.fd.io Subject: [vpp-dev] Timer expiry spikes in TW timer implementation Hi, I am trying to implement single 10sec precision periodic timer using TW. Below is the config. using the reference from test_tw_timer.c (Really helpful). tw_timer_wheel_init_2t_1w_2048sl with 0.1 sec granularity. tw_timer_start_2t_1w_2048sl with 100 as ticks. I have used the process node approach with tw_timer_expire_timers_2t_1w_2048sl check at every 0.1 sec using vlib_process_suspend(...). In the callback, timer is again started. My expectation was I would be receiving callback to expired_timer_single_callback() at every 10 sec. In actual, the callbacks are getting called at every 10sec apart. But sometimes there are some unwanted callback at irregular frequency for the same handle( i.e timer_id, pool_index). Note that this is the case either for main_core or workers. For erroneous scenarios, time diff from previous callback is inorder of ~ 0.1 ms(expected 10sec). Any pointers would of great help. Thanks, -Shaligram
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