perf_counter: add more context information

Change the callchain context entries to u16, so as to gain some space.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090406094517.457320003@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/perf_counter.h

@@ -507,10 +507,10 @@ extern void perf_counter_mmap(unsigned long addr, unsigned long len,
 extern void perf_counter_munmap(unsigned long addr, unsigned long len,
 				unsigned long pgoff, struct file *file);
 
-#define MAX_STACK_DEPTH		254
+#define MAX_STACK_DEPTH		255
 
 struct perf_callchain_entry {
-	u32	nr, hv, kernel, user;
+	u16	nr, hv, kernel, user;
 	u64	ip[MAX_STACK_DEPTH];
 };
 

kernel/perf_counter.c

@@ -1657,9 +1657,7 @@ void perf_counter_do_pending(void)
  * Callchain support -- arch specific
  */
 
-struct perf_callchain_entry *
-__attribute__((weak))
-perf_callchain(struct pt_regs *regs)
+__weak struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
 {
 	return NULL;
 }
@@ -1819,7 +1817,7 @@ void perf_counter_output(struct perf_counter *counter,
 		callchain = perf_callchain(regs);
 
 		if (callchain) {
-			callchain_size = (2 + callchain->nr) * sizeof(u64);
+			callchain_size = (1 + callchain->nr) * sizeof(u64);
 
 			header.type |= __PERF_EVENT_CALLCHAIN;
 			header.size += callchain_size;