[PATCH v2] x86/hyper-v: enable TSC page clocksource on 32bit

* [PATCH v2] x86/hyper-v: enable TSC page clocksource on 32bit
@ 2019-08-22  8:36 Vitaly Kuznetsov
  2019-08-23 15:04 ` [tip: timers/core] clocksource/drivers/hyperv: Enable " tip-bot2 for Vitaly Kuznetsov
  0 siblings, 1 reply; 2+ messages in thread
From: Vitaly Kuznetsov @ 2019-08-22  8:36 UTC (permalink / raw)
  To: linux-hyperv
  Cc: linux-kernel, x86, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
	H. Peter Anvin, K. Y. Srinivasan, Haiyang Zhang,
	Stephen Hemminger, Sasha Levin, Daniel Lezcano, Michael Kelley,
	Tianyu Lan, Peter Zijlstra

There is no particular reason to not enable TSC page clocksource
on 32-bit. mul_u64_u64_shr() is available and despite the increased
computational complexity (compared to 64bit) TSC page is still a huge
win compared to MSR-based clocksource.

In-kernel reads:
  MSR based clocksource: 3361 cycles
  TSC page clocksource: 49 cycles

Reads from userspace (utilizing vDSO in case of TSC page):
  MSR based clocksource: 5664 cycles
  TSC page clocksource: 131 cycles

Enabling TSC page on 32bits allows to get rid of CONFIG_HYPERV_TSCPAGE as
it is now not any different from CONFIG_HYPERV_TIMER.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes since v1:
- Fix a couple of nits in changelog [Michael Kelley, Thomas Gleixner]
- Fixed a comment with CONFIG_HYPERV_TSC_PAGE [Michael Kelley]
- Added Michael's Reviewed-by: tag
- Rebased on timers/core [Thomas Gleixner]
---
 arch/x86/include/asm/vdso/gettimeofday.h |  6 +++---
 drivers/clocksource/hyperv_timer.c       | 11 -----------
 drivers/hv/Kconfig                       |  3 ---
 include/clocksource/hyperv_timer.h       |  8 +++-----
 4 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/vdso/gettimeofday.h b/arch/x86/include/asm/vdso/gettimeofday.h
index ae91429129a6..bcbf901befbe 100644
--- a/arch/x86/include/asm/vdso/gettimeofday.h
+++ b/arch/x86/include/asm/vdso/gettimeofday.h
@@ -51,7 +51,7 @@ extern struct pvclock_vsyscall_time_info pvclock_page
 	__attribute__((visibility("hidden")));
 #endif
 
-#ifdef CONFIG_HYPERV_TSCPAGE
+#ifdef CONFIG_HYPERV_TIMER
 extern struct ms_hyperv_tsc_page hvclock_page
 	__attribute__((visibility("hidden")));
 #endif
@@ -192,7 +192,7 @@ static u64 vread_pvclock(void)
 }
 #endif
 
-#ifdef CONFIG_HYPERV_TSCPAGE
+#ifdef CONFIG_HYPERV_TIMER
 static u64 vread_hvclock(void)
 {
 	return hv_read_tsc_page(&hvclock_page);
@@ -215,7 +215,7 @@ static inline u64 __arch_get_hw_counter(s32 clock_mode)
 		return vread_pvclock();
 	}
 #endif
-#ifdef CONFIG_HYPERV_TSCPAGE
+#ifdef CONFIG_HYPERV_TIMER
 	if (clock_mode == VCLOCK_HVCLOCK) {
 		barrier();
 		return vread_hvclock();
diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index dad8af198e20..51b4d7ba959c 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -212,8 +212,6 @@ EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);
 struct clocksource *hyperv_cs;
 EXPORT_SYMBOL_GPL(hyperv_cs);
 
-#ifdef CONFIG_HYPERV_TSCPAGE
-
 static struct ms_hyperv_tsc_page tsc_pg __aligned(PAGE_SIZE);
 static u64 hv_sched_clock_offset __ro_after_init;
 
@@ -245,7 +243,6 @@ static struct clocksource hyperv_cs_tsc = {
 	.mask	= CLOCKSOURCE_MASK(64),
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
 };
-#endif
 
 static u64 notrace read_hv_clock_msr(struct clocksource *arg)
 {
@@ -272,7 +269,6 @@ static struct clocksource hyperv_cs_msr = {
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
-#ifdef CONFIG_HYPERV_TSCPAGE
 static bool __init hv_init_tsc_clocksource(void)
 {
 	u64		tsc_msr;
@@ -304,13 +300,6 @@ static bool __init hv_init_tsc_clocksource(void)
 
 	return true;
 }
-#else
-static bool __init hv_init_tsc_clocksource(void)
-{
-	return false;
-}
-#endif
-
 
 void __init hv_init_clocksource(void)
 {
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 9a59957922d4..79e5356a737a 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -14,9 +14,6 @@ config HYPERV
 config HYPERV_TIMER
 	def_bool HYPERV
 
-config HYPERV_TSCPAGE
-       def_bool HYPERV && X86_64
-
 config HYPERV_UTILS
 	tristate "Microsoft Hyper-V Utilities driver"
 	depends on HYPERV && CONNECTOR && NLS
diff --git a/include/clocksource/hyperv_timer.h b/include/clocksource/hyperv_timer.h
index a821deb8ecb2..422f5e5237be 100644
--- a/include/clocksource/hyperv_timer.h
+++ b/include/clocksource/hyperv_timer.h
@@ -28,12 +28,10 @@ extern void hv_stimer_cleanup(unsigned int cpu);
 extern void hv_stimer_global_cleanup(void);
 extern void hv_stimer0_isr(void);
 
-#if IS_ENABLED(CONFIG_HYPERV)
+#ifdef CONFIG_HYPERV_TIMER
 extern struct clocksource *hyperv_cs;
 extern void hv_init_clocksource(void);
-#endif /* CONFIG_HYPERV */
 
-#ifdef CONFIG_HYPERV_TSCPAGE
 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
 
 static inline notrace u64
@@ -91,7 +89,7 @@ hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
 	return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
 }
 
-#else /* CONFIG_HYPERV_TSC_PAGE */
+#else /* CONFIG_HYPERV_TIMER */
 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
 {
 	return NULL;
@@ -102,6 +100,6 @@ static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
 {
 	return U64_MAX;
 }
-#endif /* CONFIG_HYPERV_TSCPAGE */
+#endif /* CONFIG_HYPERV_TIMER */
 
 #endif
-- 
2.20.1


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