runtime: insufficient padding in the `p` structure

The current padding in the 'p' struct is hardcoded at 64 bytes. It should be the
cache line size. On ppc64x, the current value is only okay because sys.CacheLineSize
is wrong at 64 bytes. This change fixes that by making the padding equal to the
cache line size. It also fixes the cache line size for ppc64/ppc64le to 128 bytes.

Fixes #16477

Change-Id: Ib7ec5195685116eb11ba312a064f41920373d4a3
Reviewed-on: https://go-review.googlesource.com/25370Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/internal/sys/arch_ppc64.go

@@ -7,7 +7,7 @@ package sys
 const (
 	ArchFamily    = PPC64
 	BigEndian     = 1
-	CacheLineSize = 64
+	CacheLineSize = 128
 	PhysPageSize  = 65536
 	PCQuantum     = 4
 	Int64Align    = 8

src/runtime/internal/sys/arch_ppc64le.go

@@ -7,7 +7,7 @@ package sys
 const (
 	ArchFamily    = PPC64
 	BigEndian     = 0
-	CacheLineSize = 64
+	CacheLineSize = 128
 	PhysPageSize  = 65536
 	PCQuantum     = 4
 	Int64Align    = 8

src/runtime/runtime2.go

@@ -498,7 +498,7 @@ type p struct {
 
 	runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point
 
-	pad [64]byte
+	pad [sys.CacheLineSize]byte
 }
 
 const (