net: add special netFD mutex
The mutex, fdMutex, handles locking and lifetime of sysfd,
and serializes Read and Write methods.
This allows to strip 2 sync.Mutex.Lock calls,
2 sync.Mutex.Unlock calls, 1 defer and some amount
of misc overhead from every network operation.
On linux/amd64, Intel E5-2690:
benchmark old ns/op new ns/op delta
BenchmarkTCP4Persistent 9595 9454 -1.47%
BenchmarkTCP4Persistent-2 8978 8772 -2.29%
BenchmarkTCP4ConcurrentReadWrite 4900 4625 -5.61%
BenchmarkTCP4ConcurrentReadWrite-2 2603 2500 -3.96%
In general it strips 70-500 ns from every network operation depending
on processor model. On my relatively new E5-2690 it accounts to ~5%
of network op cost.
Fixes #6074.
R=golang-dev, bradfitz, alex.brainman, iant, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/12418043
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index 7d04a75..a3edb5e 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -1021,7 +1021,7 @@
bool runtime·isNaN(float64 f);
float64 runtime·ldexp(float64 d, int32 e);
float64 runtime·modf(float64 d, float64 *ip);
-void runtime·semacquire(uint32*);
+void runtime·semacquire(uint32*, bool);
void runtime·semrelease(uint32*);
int32 runtime·gomaxprocsfunc(int32 n);
void runtime·procyield(uint32);
