On 04/26/2010 10:46 AM, Glauber Costa wrote:
> This patch removes one padding byte and transform it into a flags
> field. New versions of guests using pvclock will query these flags
> upon each read.
>
Is this necessary? Why not just make the pvclock driver maintain a
local flag set, and have the HV backend call into it to update it. Why
does it need to be part of the pvclock structure?
J
> Flags, however, will only be interpreted when the guest decides to.
> It uses the pvclock_valid_flags function to signal that a specific
> set of flags should be taken into consideration. Which flags are valid
> are usually devised via HV negotiation.
>
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx>
> CC: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
> ---
> arch/x86/include/asm/pvclock-abi.h | 3 ++-
> arch/x86/include/asm/pvclock.h | 1 +
> arch/x86/kernel/pvclock.c | 9 +++++++++
> 3 files changed, 12 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
> index 6d93508..ec5c41a 100644
> --- a/arch/x86/include/asm/pvclock-abi.h
> +++ b/arch/x86/include/asm/pvclock-abi.h
> @@ -29,7 +29,8 @@ struct pvclock_vcpu_time_info {
> u64 system_time;
> u32 tsc_to_system_mul;
> s8 tsc_shift;
> - u8 pad[3];
> + u8 flags;
> + u8 pad[2];
> } __attribute__((__packed__)); /* 32 bytes */
>
> struct pvclock_wall_clock {
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index 53235fd..c50823f 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -6,6 +6,7 @@
>
> /* some helper functions for xen and kvm pv clock sources */
> cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
> +void pvclock_valid_flags(u8 flags);
> unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
> void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
> struct pvclock_vcpu_time_info *vcpu,
> diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
> index 03801f2..8f4af7b 100644
> --- a/arch/x86/kernel/pvclock.c
> +++ b/arch/x86/kernel/pvclock.c
> @@ -31,8 +31,16 @@ struct pvclock_shadow_time {
> u32 tsc_to_nsec_mul;
> int tsc_shift;
> u32 version;
> + u8 flags;
> };
>
> +static u8 valid_flags = 0;
> +
> +void pvclock_valid_flags(u8 flags)
> +{
> + valid_flags = flags;
> +}
> +
> /*
> * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
> * yielding a 64-bit result.
> @@ -91,6 +99,7 @@ static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
> dst->system_timestamp = src->system_time;
> dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
> dst->tsc_shift = src->tsc_shift;
> + dst->flags = src->flags;
> rmb(); /* test version after fetching data */
> } while ((src->version & 1) || (dst->version != src->version));
>
>
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