Commits on Mar 7, 2024

1. zebra: backpressure - Zebra push back on Buffer/Stream creation …

   Currently, the way zebra works is it creates pthread per client (BGP is
   of interest in this case) and this thread loops itself in zserv_read()
   to check for any incoming data. If there is one, then it reads,
   validates and adds it in the ibuf_fifo signalling the main thread to
   process the message. The main thread when it gets a change, processes
   the message, and invokes the function pointer registered in the header
   command. (Ex: zserv_handlers).
   
   Finally, if all of this was successful, this task reschedules itself and
   loops in zserv_read() again
   
   However, if there are already items on ibuf FIFO, that means zebra is
   slow in processing. And with the current mechanism if Zebra main is
   busy, the ibuf FIFO keeps growing holding up the memory.
   
   Show memory zebra:(Example: 15k streams hoarding ~160 MB of data)
   --- qmem libfrr ---
   Stream             :       44 variable   3432352    15042 161243800
   
   Fix:
   Client IO Thread: (zserv_read)
    - Stop doing the read events when we know there are X number of items
      on the FIFO already.(X - zebra zapi-packets <1-10000> (Default-1000)
   
    - Determine the number of items on the zserv->ibuf_fifo. Subtract this
      from the work items and only pull the number of items off that would
      take us to X items on the ibuf_fifo again.
   
    - If the number of items in the ibuf_fifo has reached to the maximum
         * Either initially when zserv_read() is called (or)
         * when processing the remainders of the incoming buffer
      the client IO thread is woken by the the zebra main.
   
   Main thread: (zserv_process_message)
   If the client ibuf always schedules a wakeup to the client IO to read
   more items from the socked buffer. This way we ensure
    - Client IO thread always tries to read the socket buffer and add more
      items to the ibuf_fifo (until max limit)
    - hidden config change (zebra zapi-packets <>) is taken into account
   
   Ticket: #3390099
   
   Signed-off-by: Donald Sharp <sharpd@nvidia.com>
   Signed-off-by: Rajasekar Raja <rajasekarr@nvidia.com>

   

   raja-rajasekar committed Mar 7, 2024
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