From 54e7b9000858c64dce3b6596287968abc2e96759 Mon Sep 17 00:00:00 2001
From: Max Rottenkolber <max@mr.gy>
Date: Wed, 15 Jun 2016 14:34:40 +0200
Subject: [PATCH 1/6] remove link.full, increase link buffer size, add
 engine.pull_npackets.

---
 src/README.md     |  6 ------
 src/core/app.lua  |  3 +++
 src/core/link.h   |  2 +-
 src/core/link.lua | 11 +----------
 4 files changed, 5 insertions(+), 17 deletions(-)

diff --git a/src/README.md b/src/README.md
index 911ebf501f..60b385d966 100644
--- a/src/README.md
+++ b/src/README.md
@@ -269,12 +269,6 @@ Predicate used to test if a link is empty. Returns true if *link* is
 empty and false otherwise.
 
 
-— Function **link.full** *link*
-
-Predicate used to test if a link is full. Returns true if *link* is full
-and false otherwise.
-
-
 — Function **link.receive** *link*
 
 Returns the next available packet (and advances the read cursor) on
diff --git a/src/core/app.lua b/src/core/app.lua
index c4fb94836c..6dc6f753aa 100644
--- a/src/core/app.lua
+++ b/src/core/app.lua
@@ -15,6 +15,9 @@ local ffi       = require("ffi")
 local C         = ffi.C
 require("core.packet_h")
 
+-- Packet per pull
+pull_npackets = math.floor(link.max / 10)
+
 -- Set to true to enable logging
 log = false
 local use_restart = false
diff --git a/src/core/link.h b/src/core/link.h
index c4ca2b45a5..83e078b144 100644
--- a/src/core/link.h
+++ b/src/core/link.h
@@ -1,6 +1,6 @@
 /* Use of this source code is governed by the Apache 2.0 license; see COPYING. */
 
-enum { LINK_RING_SIZE    = 256,
+enum { LINK_RING_SIZE    = 1001,
        LINK_MAX_PACKETS  = LINK_RING_SIZE - 1
 };
 
diff --git a/src/core/link.lua b/src/core/link.lua
index ed825e2606..32af0282f5 100644
--- a/src/core/link.lua
+++ b/src/core/link.lua
@@ -55,7 +55,7 @@ end
 
 function transmit (r, p)
 --   assert(p)
-   if full(r) then
+   if band(r.write + 1, size - 1) == r.read then
       counter.add(r.stats.txdrop)
       packet.free(p)
    else
@@ -72,11 +72,6 @@ function empty (r)
    return r.read == r.write
 end
 
--- Return true if the ring is full.
-function full (r)
-   return band(r.write + 1, size - 1) == r.read
-end
-
 -- Return the number of packets that are ready for read.
 function nreadable (r)
    if r.read > r.write then
@@ -86,10 +81,6 @@ function nreadable (r)
    end
 end
 
-function nwritable (r)
-   return max - nreadable(r)
-end
-
 function stats (r)
    local stats = {}
    for _, c

From a1f60a2fbaa2f76022e77efbaef7dc73770a9d3b Mon Sep 17 00:00:00 2001
From: Max Rottenkolber <max@mr.gy>
Date: Mon, 20 Jun 2016 19:41:22 +0200
Subject: [PATCH 2/6] Replace usage of link.full/nwritable with
 engine.pull_npackets.

---
 src/apps/basic/basic_apps.lua          | 16 ++++++----------
 src/apps/intel/intel1g.lua             |  9 ++-------
 src/apps/intel/intel_app.lua           |  6 +++---
 src/apps/ipv6/nd_light.lua             |  4 ++--
 src/apps/ipv6/ns_responder.lua         |  4 ++--
 src/apps/keyed_ipv6_tunnel/tunnel.lua  |  4 ++--
 src/apps/lwaftr/generator.lua          |  4 ++--
 src/apps/lwaftr/ipv4_apps.lua          |  6 +++---
 src/apps/lwaftr/ipv6_apps.lua          |  4 ++--
 src/apps/lwaftr/loadgen.lua            |  4 ++--
 src/apps/pcap/pcap.lua                 |  4 +++-
 src/apps/rate_limiter/rate_limiter.lua |  2 +-
 src/apps/socket/raw.lua                |  4 +++-
 src/apps/socket/unix.lua               |  6 ++++--
 src/apps/solarflare/solarflare.lua     | 14 +++++++-------
 src/apps/tap/tap.lua                   |  2 +-
 src/apps/test/lwaftr.lua               |  5 +++--
 src/apps/test/synth.lua                |  2 +-
 src/apps/virtio_net/virtio_net.lua     |  4 ++--
 src/apps/vlan/vlan.lua                 | 12 +-----------
 src/apps/vpn/vpws.lua                  |  2 +-
 src/doc/getting-started.md             | 11 +++++------
 src/program/example_spray/sprayer.lua  |  2 +-
 src/program/lisper/lisper.lua          | 11 ++++-------
 src/program/snabbmark/snabbmark.lua    |  2 +-
 25 files changed, 64 insertions(+), 80 deletions(-)

diff --git a/src/apps/basic/basic_apps.lua b/src/apps/basic/basic_apps.lua
index 10ec6e1c90..aa39889268 100644
--- a/src/apps/basic/basic_apps.lua
+++ b/src/apps/basic/basic_apps.lua
@@ -21,7 +21,7 @@ end
 
 function Source:pull ()
    for _, o in ipairs(self.output) do
-      for i = 1, link.nwritable(o) do
+      for i = 1, engine.pull_npackets do
          transmit(o, packet.clone(self.packet))
       end
    end
@@ -41,7 +41,7 @@ end
 
 function Join:push ()
    for _, inport in ipairs(self.input) do
-      for n = 1,math.min(link.nreadable(inport), link.nwritable(self.output.out)) do
+      while not link.empty(inport) do
          transmit(self.output.out, receive(inport))
       end
    end
@@ -60,7 +60,7 @@ end
 function Split:push ()
    for _, i in ipairs(self.input) do
       for _, o in ipairs(self.output) do
-         for _ = 1, math.min(link.nreadable(i), link.nwritable(o)) do
+         for _ = 1, link.nreadable(i) do
             transmit(o, receive(i))
          end
       end
@@ -95,12 +95,8 @@ end
 function Tee:push ()
    noutputs = #self.output
    if noutputs > 0 then
-      local maxoutput = link.max
-      for _, o in ipairs(self.output) do
-         maxoutput = math.min(maxoutput, link.nwritable(o))
-      end
       for _, i in ipairs(self.input) do
-         for _ = 1, math.min(link.nreadable(i), maxoutput) do
+         for _ = 1, link.nreadable(i) do
             local p = receive(i)
             maxoutput = maxoutput - 1
             do local output = self.output
@@ -122,7 +118,7 @@ function Repeater:new ()
                        {__index=Repeater})
 end
 
-function Repeater:push ()
+function Repeater:pull ()
    local i, o = self.input.input, self.output.output
    for _ = 1, link.nreadable(i) do
       local p = receive(i)
@@ -130,7 +126,7 @@ function Repeater:push ()
    end
    local npackets = #self.packets
    if npackets > 0 then
-      for i = 1, link.nwritable(o) do
+      for i = 1, engine.pull_npackets do
          assert(self.packets[self.index])
          transmit(o, packet.clone(self.packets[self.index]))
          self.index = (self.index % npackets) + 1
diff --git a/src/apps/intel/intel1g.lua b/src/apps/intel/intel1g.lua
index 74f116d0bf..3725c3557d 100644
--- a/src/apps/intel/intel1g.lua
+++ b/src/apps/intel/intel1g.lua
@@ -59,7 +59,7 @@ function Intel1g:new(conf)
    local txq = conf.txqueue or 0
    local rxq = conf.rxqueue or 0
    local ndesc = conf.ndescriptors or 512
-   local rxburst = conf.rxburst or 128
+   local rxburst = conf.rxburst or engine.pull_npackets
 
    -- 8.1.3 Register Summary, p.359
    local r = {}
@@ -589,12 +589,7 @@ function Intel1g:new(conf)
          while limit > 0 and can_receive() do
           limit = limit - 1
           if lo then					-- a link connects NIC to a sink
-           if not link.full(lo) then			-- from SolarFlareNic:pull()
-            link.transmit(lo, receive())
-           else
-            counters.pullTxLinkFull= counters.pullTxLinkFull +1
-            packet.free(receive())
-           end
+           link.transmit(lo, receive())
           else
            counters.pullNoTxLink= counters.pullNoTxLink +1
            packet.free(receive())
diff --git a/src/apps/intel/intel_app.lua b/src/apps/intel/intel_app.lua
index 2490a09798..7ce531f9f1 100644
--- a/src/apps/intel/intel_app.lua
+++ b/src/apps/intel/intel_app.lua
@@ -9,7 +9,7 @@ local lib      = require("core.lib")
 local pci      = require("lib.hardware.pci")
 local register = require("lib.hardware.register")
 local intel10g = require("apps.intel.intel10g")
-local receive, transmit, full, empty = link.receive, link.transmit, link.full, link.empty
+local receive, transmit, empty = link.receive, link.transmit, link.empty
 Intel82599 = {}
 Intel82599.__index = Intel82599
 
@@ -90,8 +90,8 @@ function Intel82599:pull ()
    local l = self.output.tx
    if l == nil then return end
    self.dev:sync_receive()
-   for i=1,128 do
-      if full(l) or not self.dev:can_receive() then break end
+   for i = 1, engine.pull_npackets do
+      if not self.dev:can_receive() then break end
       transmit(l, self.dev:receive())
    end
    self:add_receive_buffers()
diff --git a/src/apps/ipv6/nd_light.lua b/src/apps/ipv6/nd_light.lua
index 2717338d68..3c79349e76 100644
--- a/src/apps/ipv6/nd_light.lua
+++ b/src/apps/ipv6/nd_light.lua
@@ -287,7 +287,7 @@ function nd_light:push ()
    local l_in = self.input.south
    local l_out = self.output.north
    local l_reply = self.output.south
-   while not link.empty(l_in) and not link.full(l_out) do
+   while not link.empty(l_in) do
       local p = cache.p
       p[0] = link.receive(l_in)
       local status = from_south(self, p)
@@ -306,7 +306,7 @@ function nd_light:push ()
 
    l_in = self.input.north
    l_out = self.output.south
-   while not link.empty(l_in) and not link.full(l_out) do
+   while not link.empty(l_in) do
       if not self._eth_header then
          -- Drop packets until ND for the next-hop
          -- has completed.
diff --git a/src/apps/ipv6/ns_responder.lua b/src/apps/ipv6/ns_responder.lua
index a23a5151d6..3d52d187ee 100644
--- a/src/apps/ipv6/ns_responder.lua
+++ b/src/apps/ipv6/ns_responder.lua
@@ -88,7 +88,7 @@ function ns_responder:push()
    local l_in = self.input.north
    local l_out = self.output.south
    if l_in and l_out then
-      while not link.empty(l_in) and not link.full(l_out) do
+      while not link.empty(l_in) do
          -- Pass everything on north -> south
          link.transmit(l_out, link.receive(l_in))
       end
@@ -96,7 +96,7 @@ function ns_responder:push()
    l_in = self.input.south
    l_out = self.output.north
    local l_reply = self.output.south
-   while not link.empty(l_in) and not link.full(l_out) do
+   while not link.empty(l_in) do
       local p = link.receive(l_in)
       local status = process(self, p)
       if status == nil then
diff --git a/src/apps/keyed_ipv6_tunnel/tunnel.lua b/src/apps/keyed_ipv6_tunnel/tunnel.lua
index 9e394cfcfc..750979bd9b 100644
--- a/src/apps/keyed_ipv6_tunnel/tunnel.lua
+++ b/src/apps/keyed_ipv6_tunnel/tunnel.lua
@@ -180,7 +180,7 @@ function SimpleKeyedTunnel:push()
    local l_out = self.output.encapsulated
    assert(l_in and l_out)
 
-   while not link.empty(l_in) and not link.full(l_out) do
+   while not link.empty(l_in) do
       local p = link.receive(l_in)
       packet.prepend(p, self.header, HEADER_SIZE)
       local plength = ffi.cast(plength_ctype, p.data + LENGTH_OFFSET)
@@ -192,7 +192,7 @@ function SimpleKeyedTunnel:push()
    l_in = self.input.encapsulated
    l_out = self.output.decapsulated
    assert(l_in and l_out)
-   while not link.empty(l_in) and not link.full(l_out) do
+   while not link.empty(l_in) do
       local p = link.receive(l_in)
       -- match next header, cookie, src/dst addresses
       local drop = true
diff --git a/src/apps/lwaftr/generator.lua b/src/apps/lwaftr/generator.lua
index ea68d497c1..258692490c 100644
--- a/src/apps/lwaftr/generator.lua
+++ b/src/apps/lwaftr/generator.lua
@@ -138,7 +138,7 @@ end
 function from_inet:pull()
    local o = assert(self.output.output)
 
-   while not link.full(o) do
+   for i=1,engine.pull_npackets do
       if self.max_packets then
          if self.tx_packets == self.max_packets then break end
          self.tx_packets = self.tx_packets + 1
@@ -312,7 +312,7 @@ end
 function from_b4:pull()
    local o = assert(self.output.output)
 
-   while not link.full(o) do
+   for i=1,engine.pull_npackets do
       if self.max_packets then
          if self.tx_packets == self.max_packets then break end
          self.tx_packets = self.tx_packets + 1
diff --git a/src/apps/lwaftr/ipv4_apps.lua b/src/apps/lwaftr/ipv4_apps.lua
index de8709c89a..6dbac5c14c 100644
--- a/src/apps/lwaftr/ipv4_apps.lua
+++ b/src/apps/lwaftr/ipv4_apps.lua
@@ -83,7 +83,7 @@ function Reassembler:push ()
    local l2_size = self.l2_size
    local ethertype_offset = self.ethertype_offset
 
-   for _=1,math.min(link.nreadable(input), link.nwritable(output)) do
+   for _=1,link.nreadable(input) do
       local pkt = receive(input)
       if is_ipv4(pkt, ethertype_offset) and is_fragment(pkt, l2_size) then
          local frags = self:cache_fragment(pkt)
@@ -165,7 +165,7 @@ end
 function ICMPEcho:push()
    local l_in, l_out, l_reply = self.input.south, self.output.north, self.output.south
 
-   for _ = 1, math.min(link.nreadable(l_in), link.nwritable(l_out)) do
+   for _ = 1, link.nreadable(l_in) do
       local out, pkt = l_out, receive(l_in)
 
       if icmp.is_icmpv4_message(pkt, icmpv4_echo_request, 0) then
@@ -199,7 +199,7 @@ function ICMPEcho:push()
    end
 
    l_in, l_out = self.input.north, self.output.south
-   for _ = 1, math.min(link.nreadable(l_in), link.nwritable(l_out)) do
+   for _ = 1, link.nreadable(l_in) do
       transmit(l_out, receive(l_in))
    end
 end
diff --git a/src/apps/lwaftr/ipv6_apps.lua b/src/apps/lwaftr/ipv6_apps.lua
index 958fd75434..667064175f 100644
--- a/src/apps/lwaftr/ipv6_apps.lua
+++ b/src/apps/lwaftr/ipv6_apps.lua
@@ -243,7 +243,7 @@ end
 function ICMPEcho:push()
    local l_in, l_out, l_reply = self.input.south, self.output.north, self.output.south
 
-   for _ = 1, math.min(link.nreadable(l_in), link.nwritable(l_out)) do
+   for _ = 1, link.nreadable(l_in) do
       local out, pkt = l_out, receive(l_in)
 
       if icmp.is_icmpv6_message(pkt, icmpv6_echo_request, 0) then
@@ -279,7 +279,7 @@ function ICMPEcho:push()
    end
 
    l_in, l_out = self.input.north, self.output.south
-   for _ = 1, math.min(link.nreadable(l_in), link.nwritable(l_out)) do
+   for _ = 1, link.nreadable(l_in) do
       transmit(l_out, receive(l_in))
    end
 end
diff --git a/src/apps/lwaftr/loadgen.lua b/src/apps/lwaftr/loadgen.lua
index 70039388bf..eee63538bf 100644
--- a/src/apps/lwaftr/loadgen.lua
+++ b/src/apps/lwaftr/loadgen.lua
@@ -31,7 +31,7 @@ function RateLimitedRepeater:set_rate (byte_rate)
    self.rate = math.max(byte_rate, 0)
 end
 
-function RateLimitedRepeater:push ()
+function RateLimitedRepeater:pull ()
    local i, o = self.input.input, self.output.output
    for _ = 1, link.nreadable(i) do
       local p = receive(i)
@@ -50,7 +50,7 @@ function RateLimitedRepeater:push ()
 
    local npackets = #self.packets
    if npackets > 0 and self.rate > 0 then
-      for _ = 1, link.nwritable(o) do
+      for _ = 1, engine.pull_npackets do
          local p = self.packets[self.index]
          if p.length > self.bucket_content then break end
          self.bucket_content = self.bucket_content - p.length
diff --git a/src/apps/pcap/pcap.lua b/src/apps/pcap/pcap.lua
index 6edf919eec..930c4e09b8 100644
--- a/src/apps/pcap/pcap.lua
+++ b/src/apps/pcap/pcap.lua
@@ -19,7 +19,9 @@ end
 
 function PcapReader:pull ()
    assert(self.output.output)
-   while not self.done and not link.full(self.output.output) do
+   local limit = engine.pull_npackets
+   while limit > 0 and not self.done do
+      limit = limit - 1
       local data, record, extra = self.iterator()
       if data then
          local p = packet.from_string(data)
diff --git a/src/apps/rate_limiter/rate_limiter.lua b/src/apps/rate_limiter/rate_limiter.lua
index 98c1cd9347..dd1f0da811 100644
--- a/src/apps/rate_limiter/rate_limiter.lua
+++ b/src/apps/rate_limiter/rate_limiter.lua
@@ -72,7 +72,7 @@ function RateLimiter:push ()
    end
 
 
-   while not link.empty(i) and not link.full(o) do
+   while not link.empty(i) do
       local p = link.receive(i)
       local length = p.length
 
diff --git a/src/apps/socket/raw.lua b/src/apps/socket/raw.lua
index 24ad578d5d..400f403491 100644
--- a/src/apps/socket/raw.lua
+++ b/src/apps/socket/raw.lua
@@ -46,7 +46,9 @@ end
 function RawSocket:pull ()
    local l = self.output.tx
    if l == nil then return end
-   while not link.full(l) and self:can_receive() do
+   local limit = engine.pull_npackets
+   while limit > 0 and self:can_receive() do
+      limit = limit - 1
       link.transmit(l, self:receive())
    end
 end
diff --git a/src/apps/socket/unix.lua b/src/apps/socket/unix.lua
index 7b906f6ab2..57d29f2b92 100644
--- a/src/apps/socket/unix.lua
+++ b/src/apps/socket/unix.lua
@@ -148,7 +148,9 @@ function UnixSocket:new (arg)
    function self:pull()
       local l = self.output.tx
       if l == nil then return end
-      while not link.full(l) and can_receive() do
+      local limit = engine.pull_npackets
+      while limit > 0 and can_receive() do
+         limit = limit - 1
          local p = receive()
          if p then
             link.transmit(l, p) --link owns p now so we mustn't free it
@@ -197,7 +199,7 @@ function selftest ()
          pull = function(self)
             local l = self.output.tx
             if l == nil then return end
-            while not link.full(l) do
+            for i=1,engine.pull_npackets do
                local p = packet.allocate()
                ffi.copy(p.data, text)
                p.length = #text
diff --git a/src/apps/solarflare/solarflare.lua b/src/apps/solarflare/solarflare.lua
index b410bc7241..f1844cd0d8 100644
--- a/src/apps/solarflare/solarflare.lua
+++ b/src/apps/solarflare/solarflare.lua
@@ -242,19 +242,19 @@ function SolarFlareNic:pull()
    self.stats.pull = (self.stats.pull or 0) + 1
    repeat
       local n_ev = self.poll_structure.n_ev
+      local pull_npackets = engine.pull_npackets
       if n_ev > 0 then
          for i = 0, n_ev - 1 do
             local event_type = self.poll_structure.events[i].generic.type
-            if event_type == C.EF_EVENT_TYPE_RX then
+            if event_type == C.EF_EVENT_TYPE_RX and pull_npackets > 0 then
+               pull_npackets = pull_npackets - 1
                local rxpacket = self.rxpackets[self.poll_structure.events[i].rx.rq_id]
                rxpacket.length = self.poll_structure.events[i].rx.len
                self.stats.rx = (self.stats.rx or 0) + 1
-               if not link.full(self.output.tx) then
-                  link.transmit(self.output.tx, rxpacket)
-               else
-                  self.stats.link_full = (self.stats.link_full or 0) + 1
-                  packet.free(rxpacket)
-               end
+               link.transmit(self.output.tx, rxpacket)
+               self.enqueue_receive(self, self.poll_structure.events[i].rx.rq_id)
+            elseif event_type == C.EF_EVENT_TYPE_RX and pull_npackets == 0 then
+               self.stats.rxdrop = (self.stats.rxdrop or 0) + 1
                self.enqueue_receive(self, self.poll_structure.events[i].rx.rq_id)
             elseif event_type == C.EF_EVENT_TYPE_TX then
                local n_tx_done = self.poll_structure.unbundled_tx_request_ids[i].n_tx_done
diff --git a/src/apps/tap/tap.lua b/src/apps/tap/tap.lua
index 497399d11a..3b0533dfeb 100644
--- a/src/apps/tap/tap.lua
+++ b/src/apps/tap/tap.lua
@@ -34,7 +34,7 @@ end
 function Tap:pull ()
    local l = self.output.output
    if l == nil then return end
-   while not link.full(l) do
+   for i=1,engine.pull_npackets do
       local p = packet.allocate()
       local len, err = S.read(self.sock, p.data, C.PACKET_PAYLOAD_SIZE)
       -- errno == EAGAIN indicates that the read would of blocked as there is no
diff --git a/src/apps/test/lwaftr.lua b/src/apps/test/lwaftr.lua
index aec09f6f22..e8b23780c3 100644
--- a/src/apps/test/lwaftr.lua
+++ b/src/apps/test/lwaftr.lua
@@ -255,7 +255,7 @@ function Lwaftrgen:new(arg)
    return setmetatable(o, {__index=Lwaftrgen})
 end
 
-function Lwaftrgen:push ()
+function Lwaftrgen:pull ()
 
    local output = self.output.output
    local input = self.input.input
@@ -330,7 +330,8 @@ function Lwaftrgen:push ()
    self.bucket_content = self.bucket_content + self.rate * 1e6 * (cur_now - last_time)
    self.last_time = cur_now
 
-   while link.nwritable(output) > self.total_packet_count and
+   while limit > self.total_packet_count and
+      limit = limit - 1
       self.total_packet_count <= self.bucket_content do
       self.bucket_content = self.bucket_content - self.total_packet_count
 
diff --git a/src/apps/test/synth.lua b/src/apps/test/synth.lua
index 0ffc1c97fb..99a8d8dd75 100644
--- a/src/apps/test/synth.lua
+++ b/src/apps/test/synth.lua
@@ -33,7 +33,7 @@ end
 
 function Synth:pull ()
    for _, o in ipairs(self.output) do
-      for i = 1, link.nwritable(o) do
+      for i = 1, engine.pull_npackets do
          for _, p in ipairs(self.packets) do
 	    transmit(o, packet.clone(p))
 	 end
diff --git a/src/apps/virtio_net/virtio_net.lua b/src/apps/virtio_net/virtio_net.lua
index 1adadc857d..ffb6dc8c76 100644
--- a/src/apps/virtio_net/virtio_net.lua
+++ b/src/apps/virtio_net/virtio_net.lua
@@ -18,7 +18,7 @@ local main       = require("core.main")
 VirtioNet = {}
 VirtioNet.__index = VirtioNet
 
-local receive, transmit, full, nreadable, nwritable = link.receive, link.transmit, link.full, link.nreadable, link.nwritable
+local receive, transmit, nreadable = link.receive, link.transmit, link.nreadable
 
 function VirtioNet:new(args)
    return setmetatable({
@@ -51,7 +51,7 @@ function VirtioNet:pull()
    local dev = self.device
    local l = self.output.tx
    if not l then return end
-   local to_receive = math.min(nwritable(l), dev:can_receive())
+   local to_receive = math.min(engine.pull_npackets, dev:can_receive())
 
    for i=0, to_receive - 1 do
       transmit(l, dev:receive())
diff --git a/src/apps/vlan/vlan.lua b/src/apps/vlan/vlan.lua
index 763017beb8..09b6ce6e11 100644
--- a/src/apps/vlan/vlan.lua
+++ b/src/apps/vlan/vlan.lua
@@ -107,18 +107,8 @@ function VlanMux:push()
    local noutputs = #self.output
    if noutputs > 0 then
       for name, l in pairs(self.input) do
-         local maxoutput = link.max
-         -- find out max number of packets we can put out an interface
-         -- this is kind of bad because we limit ourselves by the interface with
-         -- the fullest queue, yet packets might go out a different interface. We
-         -- don't know until we've looked in the packet and parsed the VLAN id. I
-         -- suppose we kind of get some HOLB with this :(
-         for _, o in ipairs(self.output) do
-            maxoutput = math.min(maxoutput, link.nwritable(o))
-         end
-
          if type(name) == "string" then
-            for _ = 1, math.min(link.nreadable(l), maxoutput) do
+            for _ = 1, link.nreadable(l) do
                local p = receive(l)
                local ethertype = cast("uint16_t*", packet.data(p) + o_ethernet_ethertype)[0]
 
diff --git a/src/apps/vpn/vpws.lua b/src/apps/vpn/vpws.lua
index f7c5369526..f65d37a7b1 100644
--- a/src/apps/vpn/vpws.lua
+++ b/src/apps/vpn/vpws.lua
@@ -72,7 +72,7 @@ function vpws:push()
       local l_in  = self.input[port_in]
       local l_out = self.output[in_to_out[port_in]]
       assert(l_out)
-      while not link.full(l_out) and not link.empty(l_in) do
+      while not link.empty(l_in) do
          local p = link.receive(l_in)
          local datagram = self._dgram:new(p, ethernet)
          if port_in == 'customer' then
diff --git a/src/doc/getting-started.md b/src/doc/getting-started.md
index ea8a2dbc49..aa82389cc5 100644
--- a/src/doc/getting-started.md
+++ b/src/doc/getting-started.md
@@ -239,18 +239,17 @@ actually exists in order to raise an exception immediately if the app was
 not properly connected.
 
 ```
-   while not link.empty(i) and not link.full(o) do
+   while not link.empty(i) do
       self:process_packet(i, o)
       self.packet_counter = self.packet_counter + 1
    end
 end
 ```
 
-Now we loop over the available packets on `i` or until `o` is full and
-process each individually. This is a common Snabb idiom. The
-actual logic of our app is performed by a call to the `process_packet`
-method which is defined below. Note that we increment the
-`packet_counter` of our instance for every packet processed.
+Now we loop over the available packets on `i`and process each individually.
+This is a common Snabb idiom. The actual logic of our app is performed by a
+call to the `process_packet` method which is defined below. Note that we
+increment the `packet_counter` of our instance for every packet processed.
 
 ```
 function Sprayer:process_packet(i, o)
diff --git a/src/program/example_spray/sprayer.lua b/src/program/example_spray/sprayer.lua
index 51140eba84..9c206bba0f 100755
--- a/src/program/example_spray/sprayer.lua
+++ b/src/program/example_spray/sprayer.lua
@@ -13,7 +13,7 @@ function Sprayer:push()
    local i = assert(self.input.input, "input port not found")
    local o = assert(self.output.output, "output port not found")
 
-   while not link.empty(i) and not link.full(o) do
+   while not link.empty(i) do
       self:process_packet(i, o)
       self.packet_counter = self.packet_counter + 1
    end
diff --git a/src/program/lisper/lisper.lua b/src/program/lisper/lisper.lua
index 64e4f3c386..0f43e4c181 100644
--- a/src/program/lisper/lisper.lua
+++ b/src/program/lisper/lisper.lua
@@ -574,12 +574,9 @@ local function route_packet(p, rxname, txports)
             if not loc.encrypt(dp) then return end --invalid packet
          end
       end
-      if not link.full(tx) then
-         link.transmit(tx, dp)
-         stats.tx = stats.tx + 1
-      else
-         packet.free(dp)
-      end
+      link.transmit(tx, dp)
+      stats.tx = stats.tx + 1
+      packet.free(dp)
    end
 
    return p
@@ -612,7 +609,7 @@ end
 function Punt:pull()
    local tx = self.output.tx
    if tx == nil then return end
-   while not link.full(tx) do
+   for i=1,engine.pull_npackets do
       local s = get_punt_message()
       if not s then break end
       local p = packet.allocate()
diff --git a/src/program/snabbmark/snabbmark.lua b/src/program/snabbmark/snabbmark.lua
index 5dad61aaff..301d57a439 100644
--- a/src/program/snabbmark/snabbmark.lua
+++ b/src/program/snabbmark/snabbmark.lua
@@ -120,7 +120,7 @@ end
 
 function Source:pull()
    for _, o in ipairs(self.output) do
-      for i = 1, link.nwritable(o) do
+      for i = 1, engine.pull_npackets do
          local p = packet.allocate()
          ffi.copy(p.data, self.to_mac_address, 6)
          ffi.copy(p.data + 6, self.from_mac_address, 6)

From 55b157221a48dc9ffbd7fc92ae7b3b227e42cf55 Mon Sep 17 00:00:00 2001
From: Max Rottenkolber <max@mr.gy>
Date: Mon, 25 Jul 2016 15:48:24 +0200
Subject: [PATCH 3/6] Fix-up Lwaftrgen:pull and basic_apps.Tee.

---
 src/apps/basic/basic_apps.lua | 3 +--
 src/apps/test/lwaftr.lua      | 3 ++-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/apps/basic/basic_apps.lua b/src/apps/basic/basic_apps.lua
index aa39889268..94eb669272 100644
--- a/src/apps/basic/basic_apps.lua
+++ b/src/apps/basic/basic_apps.lua
@@ -93,12 +93,11 @@ function Tee:new ()
 end
 
 function Tee:push ()
-   noutputs = #self.output
+   local noutputs = #self.output
    if noutputs > 0 then
       for _, i in ipairs(self.input) do
          for _ = 1, link.nreadable(i) do
             local p = receive(i)
-            maxoutput = maxoutput - 1
             do local output = self.output
                for k = 1, #output do
                   transmit(output[k], k == #output and p or packet.clone(p))
diff --git a/src/apps/test/lwaftr.lua b/src/apps/test/lwaftr.lua
index e8b23780c3..61baf079b9 100644
--- a/src/apps/test/lwaftr.lua
+++ b/src/apps/test/lwaftr.lua
@@ -330,9 +330,10 @@ function Lwaftrgen:pull ()
    self.bucket_content = self.bucket_content + self.rate * 1e6 * (cur_now - last_time)
    self.last_time = cur_now
 
+   local limit = engine.pull_npackets
    while limit > self.total_packet_count and
-      limit = limit - 1
       self.total_packet_count <= self.bucket_content do
+      limit = limit - 1
       self.bucket_content = self.bucket_content - self.total_packet_count
 
       ipv4_hdr.dst_ip = self.b4_ipv4

From c3c34136a1381fd826e5981a0345b1206822c768 Mon Sep 17 00:00:00 2001
From: Max Rottenkolber <max@mr.gy>
Date: Mon, 25 Jul 2016 15:48:57 +0200
Subject: [PATCH 4/6] core.link.size must be a power of two.

---
 src/core/link.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/core/link.h b/src/core/link.h
index 83e078b144..f5f74488df 100644
--- a/src/core/link.h
+++ b/src/core/link.h
@@ -1,6 +1,6 @@
 /* Use of this source code is governed by the Apache 2.0 license; see COPYING. */
 
-enum { LINK_RING_SIZE    = 1001,
+enum { LINK_RING_SIZE    = 1024,
        LINK_MAX_PACKETS  = LINK_RING_SIZE - 1
 };
 

From f52861f9ece4b3d6b0741a79d84bd67f5f926e23 Mon Sep 17 00:00:00 2001
From: Max Rottenkolber <max@mr.gy>
Date: Mon, 25 Jul 2016 15:57:07 +0200
Subject: [PATCH 5/6] Revert "remove link.full", document link.nwritable,
 link.nreadable.

---
 src/README.md     | 16 ++++++++++++++++
 src/core/link.lua | 11 ++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/README.md b/src/README.md
index 60b385d966..e240cca4ee 100644
--- a/src/README.md
+++ b/src/README.md
@@ -269,6 +269,22 @@ Predicate used to test if a link is empty. Returns true if *link* is
 empty and false otherwise.
 
 
+— Function **link.full** *link*
+
+Predicate used to test if a link is full. Returns true if *link* is full
+and false otherwise.
+
+
+— Function **link.nreadable** *link*
+
+Returns the number of packets on *link*.
+
+
+— Function **link.nwriteable** *link*
+
+Returns the remaining number of packets that fit onto *link*.
+
+
 — Function **link.receive** *link*
 
 Returns the next available packet (and advances the read cursor) on
diff --git a/src/core/link.lua b/src/core/link.lua
index 32af0282f5..ed825e2606 100644
--- a/src/core/link.lua
+++ b/src/core/link.lua
@@ -55,7 +55,7 @@ end
 
 function transmit (r, p)
 --   assert(p)
-   if band(r.write + 1, size - 1) == r.read then
+   if full(r) then
       counter.add(r.stats.txdrop)
       packet.free(p)
    else
@@ -72,6 +72,11 @@ function empty (r)
    return r.read == r.write
 end
 
+-- Return true if the ring is full.
+function full (r)
+   return band(r.write + 1, size - 1) == r.read
+end
+
 -- Return the number of packets that are ready for read.
 function nreadable (r)
    if r.read > r.write then
@@ -81,6 +86,10 @@ function nreadable (r)
    end
 end
 
+function nwritable (r)
+   return max - nreadable(r)
+end
+
 function stats (r)
    local stats = {}
    for _, c

From 0214574d6afe03639b47035b2c2919f82a36f001 Mon Sep 17 00:00:00 2001
From: Max Rottenkolber <max@mr.gy>
Date: Tue, 23 Aug 2016 12:36:33 +0200
Subject: [PATCH 6/6] core.packet: make packet_t public accoding to
 documentation.

---
 src/core/packet.lua | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/core/packet.lua b/src/core/packet.lua
index 1f8fc579a8..c74631faec 100644
--- a/src/core/packet.lua
+++ b/src/core/packet.lua
@@ -13,8 +13,8 @@ local counter  = require("core.counter")
 
 require("core.packet_h")
 
-local packet_t = ffi.typeof("struct packet")
-local packet_ptr_t = ffi.typeof("struct packet *")
+packet_t = ffi.typeof("struct packet")
+local packet_ptr_t = ffi.typeof("$ *", packet_t)
 local packet_size = ffi.sizeof(packet_t)
 local header_size = 8
 max_payload = tonumber(C.PACKET_PAYLOAD_SIZE)