Commits on Mar 21, 2024

1. dhcrelay: Don't look up the ifindex for the fallback interface (sonic… …

   …-net#17797)
   
   Currently, whenever isc-dhcp-relay forwards a packet upstream,
   internally, it will try to send it on a "fallback" interface. My
   understanding is that this isn't meant to be a real interface, but
   instead is basically saying to use Linux's regular routing stack to
   route the packet appropriately (rather than having isc-dhcp-relay
   specify specifically which interface to use).
   
   The problem is that on systems with a weak CPU, a large number of
   interfaces, and many upstream servers specified, this can introduce a
   noticeable delay in packets getting sent. The delay comes from trying to
   get the ifindex of the fallback interface. In one test case, it got to
   the point that only 2 packets could be processed per second. Because of
   this, dhcrelay will easily get backlogged and likely get to a point
   where packets get dropped in the kernel.
   
   Fix this by adding a check saying if we're using the fallback interface,
   then don't try to get the ifindex of this interface. We're never going
   to have an interface named this in SONiC.
   
   Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>

   

   saiarcot895 authored and yaqiangz committed Mar 21, 2024
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