Merge #1045 (ingress-drop-nfv) into lwaftr

This also addresses the review comments from upstream #1047, noting that
the shm.exists() API changed.

src/lib/timers/ingress_drop_monitor.lua

@@ -10,6 +10,9 @@ local shm = require("core.shm")
 -- Every 100 milliseconds.
 local default_interval = 1e8
 
+local default_tips_url =
+   "https://github.com/snabbco/snabb/blob/master/src/doc/performance-tuning.md"
+
 local now = core.app.now
 
 local IngressDropMonitor = {}
@@ -19,6 +22,7 @@ function new(args)
       threshold = args.threshold or 100000,
       wait = args.wait or 20,
       action = args.action or 'flush',
+      tips_url = args.tips_url or default_tips_url,
       last_flush = 0,
       last_value = ffi.new('uint64_t[1]'),
       current_value = ffi.new('uint64_t[1]')
@@ -51,8 +55,6 @@ function IngressDropMonitor:sample ()
    end
 end
 
-local tips_url = "https://github.com/Igalia/snabb/blob/lwaftr/src/program/lwaftr/doc/README.performance.md"
-
 function IngressDropMonitor:jit_flush_if_needed ()
    if self.current_value[0] - self.last_value[0] < self.threshold then return end
    if now() - self.last_flush < self.wait then return end
@@ -63,7 +65,7 @@ function IngressDropMonitor:jit_flush_if_needed ()
    if self.action == 'flush' then
       msg = msg.."; flushing JIT to try to recover"
    end
-   msg = msg..". See "..tips_url.." for performance tuning tips."
+   msg = msg..". See "..self.tips_url.." for performance tuning tips."
    print(msg)
    if self.action == 'flush' then jit.flush() end
 end

src/program/lwaftr/run/run.lua

@@ -85,6 +85,16 @@ function parse_args(args)
    handlers["bench-file"] = function (bench_file)
       opts.bench_file = bench_file
    end
+   handlers["ingress-drop-monitor"] = function (arg)
+      if arg == 'flush' or arg == 'warn' then
+         opts.ingress_drop_monitor = arg
+      elseif arg == 'off' then
+         opts.ingress_drop_monitor = nil
+      else
+         fatal("invalid --ingress-drop-monitor argument: " .. arg
+                  .." (valid values: flush, warn, off)")
+      end
+   end
    function handlers.h() show_usage(0) end
    lib.dogetopt(args, handlers, "b:c:vD:yhir:",
       { conf = "c", v4 = 1, v6 = 1, ["v4-pci"] = 1, ["v6-pci"] = 1,

src/program/snabbnfv/traffic/traffic.lua

@@ -9,6 +9,7 @@ local ffi = require("ffi")
 local C = ffi.C
 local timer = require("core.timer")
 local pci = require("lib.hardware.pci")
+local ingress_drop_monitor = require("lib.timers.ingress_drop_monitor")
 local counter = require("core.counter")
 
 local long_opts = {
@@ -90,6 +91,7 @@ function traffic (pciaddr, confpath, sockpath)
    timer.activate(timer.new("reconf", check_for_reconfigure, 1e9, 'repeating'))
    -- Flush logs every second.
    timer.activate(timer.new("flush", io.flush, 1e9, 'repeating'))
+   timer.activate(ingress_drop_monitor.new({action='warn'}):timer())
    while true do
       needs_reconfigure = false
       print("Loading " .. confpath)