linux-kernel - [PATCH-tip v4 09/11] locking/lock_events: Don't show pvqspinlock events on bare metal

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Date:   Thu,  4 Apr 2019 13:43:18 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH-tip v4 09/11] locking/lock_events: Don't show pvqspinlock events on bare metal

On bare metail, the pvqspinlock event counts will always be 0. So there
is no point in showing their corresponding debugfs files. So they are
skipped in this case.

Signed-off-by: Waiman Long <longman@...hat.com>
Acked-by: Davidlohr Bueso <dbueso@...e.de>
---
 kernel/locking/lock_events.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/lock_events.c b/kernel/locking/lock_events.c
index 71c36d1fb834..fa2c2f951c6b 100644
--- a/kernel/locking/lock_events.c
+++ b/kernel/locking/lock_events.c
@@ -115,6 +115,29 @@ static const struct file_operations fops_lockevent = {
 	.llseek = default_llseek,
 };
 
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#include <asm/paravirt.h>
+
+static bool __init skip_lockevent(const char *name)
+{
+	static int pv_on __initdata = -1;
+
+	if (pv_on < 0)
+		pv_on = !pv_is_native_spin_unlock();
+	/*
+	 * Skip PV qspinlock events on bare metal.
+	 */
+	if (!pv_on && !memcmp(name, "pv_", 3))
+		return true;
+	return false;
+}
+#else
+static inline bool skip_lockevent(const char *name)
+{
+	return false;
+}
+#endif
+
 /*
  * Initialize debugfs for the locking event counts.
  */
@@ -133,10 +156,13 @@ static int __init init_lockevent_counts(void)
 	 * root is allowed to do the read/write to limit impact to system
 	 * performance.
 	 */
-	for (i = 0; i < lockevent_num; i++)
+	for (i = 0; i < lockevent_num; i++) {
+		if (skip_lockevent(lockevent_names[i]))
+			continue;
 		if (!debugfs_create_file(lockevent_names[i], 0400, d_counts,
 					 (void *)(long)i, &fops_lockevent))
 			goto fail_undo;
+	}
 
 	if (!debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200,
 				 d_counts, (void *)(long)LOCKEVENT_reset_cnts,
-- 
2.18.1