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x86/vmware: Read tsc_khz only once - at boot time

PATCH New Alexey Makhalov 2 participants 2 messages Oct 20, 2016 – Oct 21, 2016

Subsystems (2)
x86 VMware hypervisor interface
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Alexey Makhalov

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PATCH 1/1 x86/vmware: Read tsc_khz only once - at boot time

Re-factor the vmware platform setup code to query the hypervisor for tsc frequency only once during boot. Since the VMware hypervisor guarantees constant TSC, calibrate_tsc now uses the saved value.

Signed-off-by Alexey Makhalov <[email protected]>
Acked-by Alok N Kataria <[email protected]>
---
 arch/x86/kernel/cpu/vmware.c | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)
arch/x86/kernel/cpu/vmware.c +18 -19
index 5130985..46c7b9d 100644
@@ -48,6 +48,8 @@
 			"2"(VMWARE_HYPERVISOR_PORT), "3"(UINT_MAX) :	\
 			"memory");
 
+static unsigned long vmware_tsc_khz __ro_after_init;
+
 static inline int __vmware_platform(void)
 {
 	uint32_t eax, ebx, ecx, edx;

@@ -57,35 +59,32 @@ static inline int __vmware_platform(void)
 
 static unsigned long vmware_get_tsc_khz(void)
 {
-	uint64_t tsc_hz, lpj;
-	uint32_t eax, ebx, ecx, edx;
-
-	VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
-
-	tsc_hz = eax | (((uint64_t)ebx) << 32);
-	do_div(tsc_hz, 1000);
-	BUG_ON(tsc_hz >> 32);
-	pr_info("TSC freq read from hypervisor : %lu.%03lu MHz\n",
-			 (unsigned long) tsc_hz / 1000,
-			 (unsigned long) tsc_hz % 1000);
-
-	if (!preset_lpj) {
-		lpj = ((u64)tsc_hz * 1000);
-		do_div(lpj, HZ);
-		preset_lpj = lpj;
-	}
-
-	return tsc_hz;
+	return vmware_tsc_khz;
 }
 
 static void __init vmware_platform_setup(void)
 {
 	uint32_t eax, ebx, ecx, edx;
+	uint64_t lpj, tsc_khz;
 
 	VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
 
 	if (ebx != UINT_MAX) {
+		lpj = tsc_khz = eax | (((uint64_t)ebx) << 32);
+		do_div(tsc_khz, 1000);
+		WARN_ON(tsc_khz >> 32);
+		pr_info("TSC freq read from hypervisor : %lu.%03lu MHz\n",
+			(unsigned long) tsc_khz / 1000,
+			(unsigned long) tsc_khz % 1000);
+
+		if (!preset_lpj) {
+			do_div(lpj, HZ);
+			preset_lpj = lpj;
+		}
+
+		vmware_tsc_khz = tsc_khz;
 		x86_platform.calibrate_tsc = vmware_get_tsc_khz;
+
 #ifdef CONFIG_X86_LOCAL_APIC
 		/* Skip lapic calibration since we know the bus frequency. */
 		lapic_timer_frequency = ecx / HZ;
Signature · 1 line
1.9.1
merge bot
#1 lore raw

[tip:x86/platform] x86/vmware: Read tsc_khz only once at boot time

x86/vmware: Read tsc_khz only once at boot time
Commit-ID:  cf11372949434fc4a6194b1ed9eb861d08032d08
Gitweb:     http://git.kernel.org/tip/cf11372949434fc4a6194b1ed9eb861d08032d08
Author:     Alexey Makhalov <[email protected]>
AuthorDate: Wed, 19 Oct 2016 22:02:11 -0700
Committer:  Thomas Gleixner <[email protected]>
CommitDate: Fri, 21 Oct 2016 10:12:11 +0200

x86/vmware: Read tsc_khz only once at boot time

Re-factor the vmware platform setup code to query the hypervisor for tsc frequency only once during boot. Since the VMware hypervisor guarantees constant TSC, calibrate_tsc now uses the saved value.

Signed-off-by Alexey Makhalov <[email protected]>
Acked-by Alok N Kataria <[email protected]>
Cc [email protected]
Link http://lkml.kernel.org/r/20161020050211.GA25304@amakhalov-virtual-machine open here
Signed-off-by Thomas Gleixner <[email protected]>
---
 arch/x86/kernel/cpu/vmware.c | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)
arch/x86/kernel/cpu/vmware.c +18 -19
index 8116057..4e34da4b 100644
@@ -47,6 +47,8 @@
 			"2"(VMWARE_HYPERVISOR_PORT), "3"(UINT_MAX) :	\
 			"memory");
 
+static unsigned long vmware_tsc_khz __ro_after_init;
+
 static inline int __vmware_platform(void)
 {
 	uint32_t eax, ebx, ecx, edx;

@@ -56,35 +58,32 @@ static inline int __vmware_platform(void)
 
 static unsigned long vmware_get_tsc_khz(void)
 {
-	uint64_t tsc_hz, lpj;
-	uint32_t eax, ebx, ecx, edx;
-
-	VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
-
-	tsc_hz = eax | (((uint64_t)ebx) << 32);
-	do_div(tsc_hz, 1000);
-	BUG_ON(tsc_hz >> 32);
-	pr_info("TSC freq read from hypervisor : %lu.%03lu MHz\n",
-			 (unsigned long) tsc_hz / 1000,
-			 (unsigned long) tsc_hz % 1000);
-
-	if (!preset_lpj) {
-		lpj = ((u64)tsc_hz * 1000);
-		do_div(lpj, HZ);
-		preset_lpj = lpj;
-	}
-
-	return tsc_hz;
+	return vmware_tsc_khz;
 }
 
 static void __init vmware_platform_setup(void)
 {
 	uint32_t eax, ebx, ecx, edx;
+	uint64_t lpj, tsc_khz;
 
 	VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
 
 	if (ebx != UINT_MAX) {
+		lpj = tsc_khz = eax | (((uint64_t)ebx) << 32);
+		do_div(tsc_khz, 1000);
+		WARN_ON(tsc_khz >> 32);
+		pr_info("TSC freq read from hypervisor : %lu.%03lu MHz\n",
+			(unsigned long) tsc_khz / 1000,
+			(unsigned long) tsc_khz % 1000);
+
+		if (!preset_lpj) {
+			do_div(lpj, HZ);
+			preset_lpj = lpj;
+		}
+
+		vmware_tsc_khz = tsc_khz;
 		x86_platform.calibrate_tsc = vmware_get_tsc_khz;
+
 #ifdef CONFIG_X86_LOCAL_APIC
 		/* Skip lapic calibration since we know the bus frequency. */
 		lapic_timer_frequency = ecx / HZ;