diff --git a/beacon_chain/eth2_processor.nim b/beacon_chain/eth2_processor.nim
index 1579a9860..43df92dd2 100644
--- a/beacon_chain/eth2_processor.nim
+++ b/beacon_chain/eth2_processor.nim
@@ -1,7 +1,16 @@
+# beacon_chain
+# Copyright (c) 2018-2021 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+{.push raises: [Defect].}
+
 import
   std/[math, tables],
   stew/results,
-  chronicles, chronicles/chronos_tools, chronos, metrics,
+  chronicles, chronos, metrics,
   ./spec/[crypto, datatypes, digest],
   ./block_pools/[clearance, chain_dag],
   ./attestation_aggregation, ./exit_pool,
@@ -234,6 +243,8 @@ proc processBlock(self: var Eth2Processor, entry: BlockEntry) =
     if entry.v.resFut != nil:
       entry.v.resFut.complete(Result[void, BlockError].err(res.error()))
 
+{.pop.} # TODO AsyncQueue.addLast raises Exception in theory but not in practise
+
 proc blockValidator*(
     self: var Eth2Processor,
     signedBlock: SignedBeaconBlock): ValidationResult =
@@ -280,11 +291,13 @@ proc blockValidator*(
   # sync, we don't lose the gossip blocks, but also don't block the gossip
   # propagation of seemingly good blocks
   trace "Block validated"
-  traceAsyncErrors self.blocksQueue.addLast(
+  asyncSpawn self.blocksQueue.addLast(
     BlockEntry(v: SyncBlock(blk: signedBlock)))
 
   ValidationResult.Accept
 
+{.push raises: [Defect].}
+
 proc attestationValidator*(
     self: var Eth2Processor,
     attestation: Attestation,
@@ -321,14 +334,14 @@ proc attestationValidator*(
       notice "Queue full, dropping attestation",
         dropped = shortLog(self.attestationsQueue[0].v)
       discard self.attestationsQueue.popFirstNoWait()
-    except CatchableError as exc:
+    except AsyncQueueEmptyError as exc:
       raiseAssert "If queue is full, we have at least one item! " & exc.msg
 
   trace "Attestation validated"
   try:
     self.attestationsQueue.addLastNoWait(
       AttestationEntry(v: attestation, attesting_indices: v.get()))
-  except CatchableError as exc:
+  except AsyncQueueFullError as exc:
     raiseAssert "We just checked that queue is not full! " & exc.msg
 
   ValidationResult.Accept
@@ -373,7 +386,7 @@ proc aggregateValidator*(
       notice "Queue full, dropping aggregate",
         dropped = shortLog(self.aggregatesQueue[0].v)
       discard self.aggregatesQueue.popFirstNoWait()
-    except CatchableError as exc:
+    except AsyncQueueEmptyError as exc:
       raiseAssert "We just checked that queue is not full! " & exc.msg
 
   trace "Aggregate validated",
@@ -385,7 +398,7 @@ proc aggregateValidator*(
     self.aggregatesQueue.addLastNoWait(AggregateEntry(
       v: signedAggregateAndProof.message.aggregate,
       attesting_indices: v.get()))
-  except CatchableError as exc:
+  except AsyncQueueFullError as exc:
     raiseAssert "We just checked that queue is not full! " & exc.msg
 
   ValidationResult.Accept
@@ -435,6 +448,8 @@ proc voluntaryExitValidator*(
 
   ValidationResult.Accept
 
+{.pop.} # TODO raises in chronos
+
 proc runQueueProcessingLoop*(self: ref Eth2Processor) {.async.} =
   # Blocks in eth2 arrive on a schedule for every slot:
   #
@@ -448,24 +463,36 @@ proc runQueueProcessingLoop*(self: ref Eth2Processor) {.async.} =
     attestationFut = self[].attestationsQueue.popFirst()
 
   while true:
-    trace "Waiting for processing work"
-    await blockFut or aggregateFut or attestationFut
+    # Cooperative concurrency: one idle calculation step per loop - because
+    # we run both networking and CPU-heavy things like block processing
+    # on the same thread, we need to make sure that there is steady progress
+    # on the networking side or we get long lockups that lead to timeouts.
+    #
+    # We cap waiting for an idle slot to 1 second in case there's a lot of
+    # network traffic taking up all CPU - we don't want to _completely_ stop
+    # processing blocks in this case (attestations will get dropped)
+    discard await idleAsync().withTimeout(1.seconds)
 
-    while blockFut.finished:
-      # TODO await here _hopefully_ yields to the event loop allowing another
-      #      queue put to complete
-      self[].processBlock(await blockFut)
+    # Avoid one more `await` when there's work to do
+    if not (blockFut.finished or aggregateFut.finished or attestationFut.finished):
+      trace "Waiting for processing work"
+      await blockFut or aggregateFut or attestationFut
+
+    # Only run one task per idle iteration, in priority order: blocks are needed
+    # for all other processing - then come aggregates which are cheap to
+    # process but might have a big impact on fork choice - last come
+    # attestations which individually have the smallest effect on chain progress
+    if blockFut.finished:
+      self[].processBlock(blockFut.read())
       blockFut = self[].blocksQueue.popFirst()
-
-    if aggregateFut.finished:
-      self[].processAggregate(await aggregateFut)
+    elif aggregateFut.finished:
+      # aggregates will be dropped under heavy load on producer side
+      self[].processAggregate(aggregateFut.read())
       aggregateFut = self[].aggregatesQueue.popFirst()
-      continue
-
-    if attestationFut.finished:
-      self[].processAttestation(await attestationFut)
+    elif attestationFut.finished:
+      # attestations will be dropped under heavy load on producer side
+      self[].processAttestation(attestationFut.read())
       attestationFut = self[].attestationsQueue.popFirst()
-      continue
 
 proc new*(T: type Eth2Processor,
           config: BeaconNodeConf,
diff --git a/vendor/nim-chronos b/vendor/nim-chronos
index 46c0bf3c5..396208044 160000
--- a/vendor/nim-chronos
+++ b/vendor/nim-chronos
@@ -1 +1 @@
-Subproject commit 46c0bf3c5aff131ac437a88c00aa112133c94d54
+Subproject commit 396208044a6375d7d803f1dce6b2d1efdfec7fbb