Revert "perf/x86/intel, watchdog: Switch NMI watchdog to ref cycles on x86"

This reverts commit 2c95afc1e83d93fac3be6923465e1753c2c53b0a.

Stephane reported the following regression:

> Since Andi added:
>
> commit 2c95afc1e83d93fac3be6923465e1753c2c53b0a
> Author: Andi Kleen <[e-mail]>
> Date: Thu Jun 9 06:14:38 2016 -0700
>
> perf/x86/intel, watchdog: Switch NMI watchdog to ref cycles on x86
>
> $ perf stat -e ref-cycles ls
> <not counted> ....
>
> fails systematically because the ref-cycles is now used by the
> watchdog and given this is a system-wide pinned event, it monopolizes
> the fixed counter 2 which is the only counter able to measure this event.

Since the next merge window is near, fix the regression for now
by reverting the commit.

Reported-by: Stephane Eranian <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Vince Weaver <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/apic/hw_nmi.c

···
 #include <linux/nmi.h>
 #include <linux/module.h>
 #include <linux/delay.h>
-#include <linux/perf_event.h>
 
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
-int hw_nmi_get_event(void)
-{
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
-		return PERF_COUNT_HW_REF_CPU_CYCLES;
-	return PERF_COUNT_HW_CPU_CYCLES;
-}
-
 u64 hw_nmi_get_sample_period(int watchdog_thresh)
 {
 	return (u64)(cpu_khz) * 1000 * watchdog_thresh;

include/linux/nmi.h

···
 
 #ifdef CONFIG_LOCKUP_DETECTOR
 u64 hw_nmi_get_sample_period(int watchdog_thresh);
-int hw_nmi_get_event(void);
 extern int nmi_watchdog_enabled;
 extern int soft_watchdog_enabled;
 extern int watchdog_user_enabled;

kernel/watchdog.c

···
 
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 
-/* Can be overriden by architecture */
-__weak int hw_nmi_get_event(void)
-{
-	return PERF_COUNT_HW_CPU_CYCLES;
-}
-
 static struct perf_event_attr wd_hw_attr = {
 	.type		= PERF_TYPE_HARDWARE,
 	.config		= PERF_COUNT_HW_CPU_CYCLES,
···
 
 	wd_attr = &wd_hw_attr;
 	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
-	wd_attr->config = hw_nmi_get_event();
 
 	/* Try to register using hardware perf events */
 	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);