Re: [PATCH 2/5] Make xen use the paravirt clocksource structs and functions.

[Jeremy Fitzhardinge <jeremy@goop.org>]

Gerd Hoffmann wrote:
> This patch updates the xen guest to use the pvclock structs
> and helper functions.
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  arch/x86/xen/Kconfig        |    1 +
>  arch/x86/xen/time.c         |  130 ++++---------------------------------------
>  include/xen/interface/xen.h |    5 +-
>  3 files changed, 14 insertions(+), 122 deletions(-)
>
> diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
> index 2e641be..3a4f16a 100644
> --- a/arch/x86/xen/Kconfig
> +++ b/arch/x86/xen/Kconfig
> @@ -5,6 +5,7 @@
>  config XEN
>  	bool "Xen guest support"
>  	select PARAVIRT
> +	select PARAVIRT_CLOCK
>  	depends on X86_32
>  	depends on X86_CMPXCHG && X86_TSC && !(X86_VISWS || X86_VOYAGER)
>  	help
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index c39e1a5..bf31fb5 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -13,6 +13,7 @@
>  #include <linux/clockchips.h>
>  #include <linux/kernel_stat.h>
>  
> +#include <asm/pvclock.h>
>  #include <asm/xen/hypervisor.h>
>  #include <asm/xen/hypercall.h>
>  
> @@ -30,17 +31,6 @@
>  
>  static cycle_t xen_clocksource_read(void);
>  
> -/* These are perodically updated in shared_info, and then copied here. */
> -struct shadow_time_info {
> -	u64 tsc_timestamp;     /* TSC at last update of time vals.  */
> -	u64 system_timestamp;  /* Time, in nanosecs, since boot.    */
> -	u32 tsc_to_nsec_mul;
> -	int tsc_shift;
> -	u32 version;
> -};
> -
> -static DEFINE_PER_CPU(struct shadow_time_info, shadow_time);
> -
>  /* runstate info updated by Xen */
>  static DEFINE_PER_CPU(struct vcpu_runstate_info, runstate);
>  
> @@ -230,121 +220,26 @@ unsigned long xen_cpu_khz(void)
>  	return xen_khz;
>  }
>  
> -/*
> - * Reads a consistent set of time-base values from Xen, into a shadow data
> - * area.
> - */
> -static unsigned get_time_values_from_xen(void)
> -{
> -	struct vcpu_time_info   *src;
> -	struct shadow_time_info *dst;
> -
> -	/* src is shared memory with the hypervisor, so we need to
> -	   make sure we get a consistent snapshot, even in the face of
> -	   being preempted. */
> -	src = &__get_cpu_var(xen_vcpu)->time;
> -	dst = &__get_cpu_var(shadow_time);
> -
> -	do {
> -		dst->version = src->version;
> -		rmb();		/* fetch version before data */
> -		dst->tsc_timestamp     = src->tsc_timestamp;
> -		dst->system_timestamp  = src->system_time;
> -		dst->tsc_to_nsec_mul   = src->tsc_to_system_mul;
> -		dst->tsc_shift         = src->tsc_shift;
> -		rmb();		/* test version after fetching data */
> -	} while ((src->version & 1) | (dst->version ^ src->version));
> -
> -	return dst->version;
> -}
> -
> -/*
> - * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
> - * yielding a 64-bit result.
> - */
> -static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
> -{
> -	u64 product;
> -#ifdef __i386__
> -	u32 tmp1, tmp2;
> -#endif
> -
> -	if (shift < 0)
> -		delta >>= -shift;
> -	else
> -		delta <<= shift;
> -
> -#ifdef __i386__
> -	__asm__ (
> -		"mul  %5       ; "
> -		"mov  %4,%%eax ; "
> -		"mov  %%edx,%4 ; "
> -		"mul  %5       ; "
> -		"xor  %5,%5    ; "
> -		"add  %4,%%eax ; "
> -		"adc  %5,%%edx ; "
> -		: "=A" (product), "=r" (tmp1), "=r" (tmp2)
> -		: "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
> -#elif __x86_64__
> -	__asm__ (
> -		"mul %%rdx ; shrd $32,%%rdx,%%rax"
> -		: "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
> -#else
> -#error implement me!
> -#endif
> -
> -	return product;
> -}
> -
> -static u64 get_nsec_offset(struct shadow_time_info *shadow)
> -{
> -	u64 now, delta;
> -	now = native_read_tsc();
> -	delta = now - shadow->tsc_timestamp;
> -	return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
> -}
> -
>  static cycle_t xen_clocksource_read(void)
>  {
> -	struct shadow_time_info *shadow = &get_cpu_var(shadow_time);
> +        struct vcpu_time_info *src;
>  	cycle_t ret;
> -	unsigned version;
> -
> -	do {
> -		version = get_time_values_from_xen();
> -		barrier();
> -		ret = shadow->system_timestamp + get_nsec_offset(shadow);
> -		barrier();
> -	} while (version != __get_cpu_var(xen_vcpu)->time.version);
> -
> -	put_cpu_var(shadow_time);
>  
> +	src = &get_cpu_var(xen_vcpu)->time;
> +	ret = pvclock_clocksource_read((void*)src);
> +	put_cpu_var(xen_vcpu);
>  	return ret;
>  }
>  
>  static void xen_read_wallclock(struct timespec *ts)
>  {
> -	const struct shared_info *s = HYPERVISOR_shared_info;
> -	u32 version;
> -	u64 delta;
> -	struct timespec now;
> -
> -	/* get wallclock at system boot */
> -	do {
> -		version = s->wc_version;
> -		rmb();		/* fetch version before time */
> -		now.tv_sec  = s->wc_sec;
> -		now.tv_nsec = s->wc_nsec;
> -		rmb();		/* fetch time before checking version */
> -	} while ((s->wc_version & 1) | (version ^ s->wc_version));
> +	struct shared_info *s = HYPERVISOR_shared_info;
> +	struct pvclock_wall_clock *wall_clock = &(s->wc);
> +        struct vcpu_time_info *vcpu_time;
>  
> -	delta = xen_clocksource_read();	/* time since system boot */
> -	delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
> -
> -	now.tv_nsec = do_div(delta, NSEC_PER_SEC);
> -	now.tv_sec = delta;
> -
> -	set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
> +	vcpu_time = &get_cpu_var(xen_vcpu)->time;
> +	pvclock_read_wallclock(wall_clock, (void*)vcpu_time, ts);
>   

Why this cast here?  Because the corresponding struct in vcpu_info 
hasn't been updated to match?

    J