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

[Michael Kelley]

From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Sent: Wednesday, August 21, 2019 2:57 AM
> 
> 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 (unilizing vDSO in case of TSC page):

s/unilizing/utilizing/

>   MSR based clocksource: 5664 cycles
>   TSC page clocksource: 131 cycles
> 
> Enabling TSC page on 32bits allows us to get rid of CONFIG_HYPERV_TSCPAGE
> as it is now not any different from CONFIG_HYPERV_TIMER.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/vdso/gettimeofday.h |  6 +++---
>  drivers/clocksource/hyperv_timer.c       | 11 -----------
>  drivers/hv/Kconfig                       |  3 ---
>  include/clocksource/hyperv_timer.h       |  6 ++----
>  4 files changed, 5 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/x86/include/asm/vdso/gettimeofday.h
> b/arch/x86/include/asm/vdso/gettimeofday.h
> index ba71a63cdac4..e9ee139cf29e 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
> @@ -228,7 +228,7 @@ 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);
> @@ -251,7 +251,7 @@ 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 ba2c79e6a0ee..b6083faab540 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;
> 
>  struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
> @@ -244,7 +242,6 @@ static struct clocksource hyperv_cs_tsc = {
>  	.mask	= CLOCKSOURCE_MASK(64),
>  	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
>  };
> -#endif
> 
>  static u64 notrace read_hv_sched_clock_msr(void)
>  {
> @@ -271,7 +268,6 @@ 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;
> @@ -306,13 +302,6 @@ static bool __init hv_init_tsc_clocksource(void)
>  	sched_clock_register(read_hv_sched_clock_tsc, 64, HV_CLOCK_HZ);
>  	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..f72e4619d0a7 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
> @@ -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 */

There's a #else prior to the #endif that has TSCPAGE misspelled
as TSC_PAGE in the comment.  Should probably fix the comment ...

> 
>  #endif
> --
> 2.20.1

Overall an excellent removal of unnecessary complexity.  Thx.
Two minor nits notwithstanding,

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>