code review 6223050: runtime: faster GC mark phase

src/pkg/runtime/malloc.h

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Memory allocator, based on tcmalloc.
 // http://goog-perftools.sourceforge.net/doc/tcmalloc.html
 
 // The main allocator works in runs of pages.
 // Small allocation sizes (up to and including 32 kB) are
 // rounded to one of about 100 size classes, each of which
@@ skipping 106 matching lines @@
         // On 32-bit, we don't bother limiting anything: 20 bits for 4G.
 #ifdef _64BIT
         MHeapMap_Bits = 22,
 #else
         MHeapMap_Bits = 20,
 #endif
 
         // Max number of threads to run garbage collection.
         // 2, 3, and 4 are all plausible maximums depending
         // on the hardware details of the machine.  The garbage
-        // collector scales well to 4 cpus.
-        MaxGcproc = 4,
+        // collector scales well to 8 cpus.
+        MaxGcproc = 8,
 };
 
 // A generic linked list of blocks.  (Typically the block is bigger than sizeof(MLink).)
 struct MLink
 {
         MLink *next;
 };
 
 // SysAlloc obtains a large chunk of zeroed memory from the
 // operating system, typically on the order of a hundred kilobytes
@@ skipping 274 matching lines @@
 
 void    runtime·MProf_Malloc(void*, uintptr);
 void    runtime·MProf_Free(void*, uintptr);
 void    runtime·MProf_GC(void);
 int32   runtime·gcprocs(void);
 void    runtime·helpgc(int32 nproc);
 void    runtime·gchelper(void);
 
 bool    runtime·getfinalizer(void *p, bool del, void (**fn)(void*), int32 *nret);
 void    runtime·walkfintab(void (*fn)(void*));