perf_events: Optimize the swcounter hotpath

The structure init creates a bit memcpy, which shows
up big time in perf annotate output:

          :      ffffffff810a859d <__perf_sw_event>:
     1.68 :      ffffffff810a859d:       55                      push   %rbp
     1.69 :      ffffffff810a859e:       41 89 fa                mov    %edi,%r10d
     0.01 :      ffffffff810a85a1:       49 89 c9                mov    %rcx,%r9
     0.00 :      ffffffff810a85a4:       31 c0                   xor    %eax,%eax
     1.71 :      ffffffff810a85a6:       b9 16 00 00 00          mov    $0x16,%ecx
     0.00 :      ffffffff810a85ab:       48 89 e5                mov    %rsp,%rbp
     0.00 :      ffffffff810a85ae:       48 83 ec 60             sub    $0x60,%rsp
     1.52 :      ffffffff810a85b2:       48 8d 7d a0             lea    -0x60(%rbp),%rdi
    85.20 :      ffffffff810a85b6:       f3 ab                   rep stos %eax,%es:(%rdi)

None of the callees depends on the structure being pre-initialized,
so only initialize ->addr. This gets rid of the memcpy overhead.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/perf_event.c

@@ -3954,12 +3954,12 @@ static void do_perf_sw_event(enum perf_type_id type, u32 event_id,
 void __perf_sw_event(u32 event_id, u64 nr, int nmi,
 			    struct pt_regs *regs, u64 addr)
 {
-	struct perf_sample_data data = {
-		.addr = addr,
-	};
+	struct perf_sample_data data;
 
-	do_perf_sw_event(PERF_TYPE_SOFTWARE, event_id, nr, nmi,
-				&data, regs);
+	data.addr = addr;
+	data.raw  = NULL;
+
+	do_perf_sw_event(PERF_TYPE_SOFTWARE, event_id, nr, nmi, &data, regs);
 }
 
 static void perf_swevent_read(struct perf_event *event)