Re: [RFC 5/7] kvm steal time implementation

[Rik van Riel <riel@redhat.com>]

On 08/25/2010 05:43 PM, Glauber Costa wrote:
> This is the proposed kvm-side steal time implementation.
> It is migration safe, as it checks flags at every read.
>
> Signed-off-by: Glauber Costa<glommer@redhat.com>
> ---
>   arch/x86/kernel/kvmclock.c |   35 +++++++++++++++++++++++++++++++++++
>   1 files changed, 35 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index eb9b76c..a1f4852 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -18,6 +18,8 @@
>
>   #include<linux/clocksource.h>
>   #include<linux/kvm_para.h>
> +#include<linux/kernel_stat.h>
> +#include<linux/sched.h>
>   #include<asm/pvclock.h>
>   #include<asm/msr.h>
>   #include<asm/apic.h>
> @@ -41,6 +43,7 @@ early_param("no-kvmclock", parse_no_kvmclock);
>
>   /* The hypervisor will put information about time periodically here */
>   static DEFINE_PER_CPU_SHARED_ALIGNED(struct pvclock_vcpu_time_info, hv_clock);
> +static DEFINE_PER_CPU(u64, steal_info);
>   static struct pvclock_wall_clock wall_clock;
>
>   /*
> @@ -82,6 +85,32 @@ static cycle_t kvm_clock_read(void)
>   	return ret;
>   }
>
> +static DEFINE_PER_CPU(u64, steal_info);
> +
> +cputime_t kvm_get_steal_time(void)
> +{
> +	u64 delta = 0;
> +	u64 *last_steal_info, this_steal_info;
> +	struct pvclock_vcpu_time_info *src;
> +
> +	src =&get_cpu_var(hv_clock);
> +	if (!(src->flags&  PVCLOCK_STEAL_BIT))
> +		goto out;
> +
> +	this_steal_info = src->steal_time;
> +	put_cpu_var(hv_clock);
> +
> +	last_steal_info =&get_cpu_var(steal_info);
> +
> +	delta = this_steal_info - *last_steal_info;
> +
> +	*last_steal_info = this_steal_info;
> +	put_cpu_var(steal_info);
> +
> +out:
> +	return msecs_to_cputime(delta);
> +}

Can this be changed to properly deal with overflow in
src->steal_time, the same way we deal with (eg jiffie)
overflow elsewhere in the kernel?

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