linux-kernel - [PATCH 4/4] hwmon: (dell-smm) Measure time duration of SMM call around inlined asm

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Date:   Sat, 27 Jan 2018 17:23:51 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Jonathan Buzzard <jonathan@...zard.org.uk>,
        Mario Limonciello <mario.limonciello@...l.com>
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pali Rohár <pali.rohar@...il.com>
Subject: [PATCH 4/4] hwmon: (dell-smm) Measure time duration of SMM call around inlined asm

Measure only inlined asm code, not other functions to have as precise as
possible measured time.

Signed-off-by: Pali Rohár <pali.rohar@...il.com>
---
 drivers/hwmon/dell-smm-hwmon.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index bf3bb7e1adab..e001afd53f46 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -147,14 +147,16 @@ static int i8k_smm_func(void *par)
 	int ebx = regs->ebx;
 	unsigned long duration;
 	ktime_t calltime, delta, rettime;
-
-	calltime = ktime_get();
 #endif
 
 	/* SMM requires CPU 0 */
 	if (smp_processor_id() != 0)
 		return -EBUSY;
 
+#ifdef DEBUG
+	calltime = ktime_get();
+#endif
+
 #if defined(CONFIG_X86_64)
 	asm volatile("pushq %%rax\n\t"
 		"movl 0(%%rax),%%edx\n\t"
@@ -208,13 +210,17 @@ static int i8k_smm_func(void *par)
 	    :    "a"(regs)
 	    :    "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
 #endif
-	if (rc != 0 || (regs->eax & 0xffff) == 0xffff || regs->eax == eax)
-		rc = -EINVAL;
 
 #ifdef DEBUG
 	rettime = ktime_get();
 	delta = ktime_sub(rettime, calltime);
 	duration = ktime_to_ns(delta) >> 10;
+#endif
+
+	if (rc != 0 || (regs->eax & 0xffff) == 0xffff || regs->eax == eax)
+		rc = -EINVAL;
+
+#ifdef DEBUG
 	pr_debug("smm(0x%.4x 0x%.4x) = 0x%.4x  (took %7lu usecs)\n", eax, ebx,
 		(rc ? 0xffff : regs->eax & 0xffff), duration);
 #endif
-- 
2.11.0