tune attestation params (#2301)

* a little bit more priority to attestation processing
* better implementation for bytes_to_uint64

beacon_chain/eth2_processor.nim

@@ -500,12 +500,18 @@ proc runQueueProcessingLoop*(self: ref Eth2Processor) {.async.} =
     # 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.
-    #
+    const
       # We cap waiting for an idle slot 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) - doing so also allows us
       # to benefit from more batching / larger network reads when under load.
-    discard await idleAsync().withTimeout(10.milliseconds)
+      idleTimeout = 10.milliseconds
+
+      # Attestation processing is fairly quick and therefore done in batches to
+      # avoid some of the `Future` overhead
+      attestationBatch = 16
+
+    discard await idleAsync().withTimeout(idleTimeout)
 
     # Avoid one more `await` when there's work to do
     if not (blockFut.finished or aggregateFut.finished or attestationFut.finished):
@@ -522,7 +528,7 @@ proc runQueueProcessingLoop*(self: ref Eth2Processor) {.async.} =
     elif aggregateFut.finished:
       # aggregates will be dropped under heavy load on producer side
       self[].processAggregate(aggregateFut.read())
-      for i in 0..<7: # process a few at a time - this is fairly fast
+      for i in 0..<attestationBatch: # process a few at a time - this is fairly fast
         if self[].aggregatesQueue.empty():
           break
         self[].processAggregate(self[].aggregatesQueue.popFirstNoWait())
@@ -532,7 +538,7 @@ proc runQueueProcessingLoop*(self: ref Eth2Processor) {.async.} =
       # attestations will be dropped under heavy load on producer side
       self[].processAttestation(attestationFut.read())
 
-      for i in 0..<7: # process a few at a time - this is fairly fast
+      for i in 0..<attestationBatch: # process a few at a time - this is fairly fast
         if self[].attestationsQueue.empty():
           break
         self[].processAttestation(self[].attestationsQueue.popFirstNoWait())

beacon_chain/spec/helpers.nim

@@ -86,9 +86,7 @@ func bytes_to_uint64*(data: openArray[byte]): uint64 =
   doAssert data.len == 8
 
   # Little-endian data representation
-  result = 0
-  for i in countdown(7, 0):
-    result = result * 256 + data[i]
+  uint64.fromBytesLE(data)
 
 # Have 1, 4, and 8-byte versions. Spec only defines 8-byte version, but useful
 # to check invariants on rest.