X ... but negative impact on separate client / server processes, strange ...

without runtime.Gosched

null:00   ; oid=0..16995  nread=68269354  t=536.560158ms (31.569µs / object)  x=zsha1.go
null:00   ; oid=0..16995  nread=68269354  t=532.416867ms (31.326µs / object)  x=zsha1.go
null:00   ; oid=0..16995  nread=68269354  t=536.958977ms (31.593µs / object)  x=zsha1.go
null:00   ; oid=0..16995  nread=68269354  t=534.170594ms (31.429µs / object)  x=zsha1.go

with runtime.Gosched

null:00   ; oid=0..16995  nread=68269354  t=594.966346ms (35.006µs / object)  x=zsha1.go
null:00   ; oid=0..16995  nread=68269354  t=597.510359ms (35.155µs / object)  x=zsha1.go
null:00   ; oid=0..16995  nread=68269354  t=598.251026ms (35.199µs / object)  x=zsha1.go
null:00   ; oid=0..16995  nread=68269354  t=596.02138ms (35.068µs / object)  x=zsha1.go

----

-> trace shows runtime.Gosched indeed switches to woken up G without
second syscall in serveRecv but serveRecv migrates to different M (so
different CPU)

go/neo/connection.go

@@ -29,7 +29,7 @@ import (
 	"math"
 	"net"
 	"reflect"
-	"runtime"
+	//"runtime"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -791,7 +791,7 @@ func (nl *NodeLink) serveRecv() {
 		// By default proc runq will execute only when sendRecv blocks
 		// next time deep in nl.recvPkt(), but let's force the switch
 		// now without additional wating to reduce latency.
-		runtime.Gosched()
+		//runtime.Gosched()
 /*
 		// XXX goes away in favour of .rxdownFlag; reasons
 		// - no need to reallocate rxdown for light conn