On Mon, 2008-07-07 at 15:56 +0200, ehrhardt@xxxxxxxxxxxxxxxxxx wrote:
> From: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
>
> The current implementation of kvmtrace uses always a 64 bit cycle variable,
> but get_cycles() which is used to fill it is "unsigned long" which might be 32
> bit.
> This reduces the accuracy e.g. on embedded powerpc since we would have a 64bit
> value but get_cycle() only returns the low 32 bit.
> To solve that this patch introduces kvm_arch_trace_cycles() which allows us
> to make this calculation architecture aware. That way every architecture can
> insert whatever fits best for their "kvmtrace cycle counter".
>
> Signed-off-by: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
Just one comment below...
BTW, because this breaks the ia64 and s390 builds, it might be nice to
CC the appropriate list/maintainer directly.
> ---
>
> [diffstat]
> arch/powerpc/kvm/powerpc.c | 25 +++++++++++++++++++++++++
> arch/x86/kvm/x86.c | 5 +++++
> include/linux/kvm_host.h | 2 ++
> virt/kvm/kvm_trace.c | 2 +-
> 4 files changed, 33 insertions(+), 1 deletion(-)
>
> [diff]
>
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -521,6 +521,31 @@
> return r;
> }
>
> +/*
> + * We need a 64 bit value here and the default get_cycles has only 32bit (tbl)
> + * on 32bit ppc. Since we have a 64bit counter for that we provide it here in
> + * full resolution for the trace records.
> +*/
> +__u64 kvm_arch_trace_cycles()
> +{
> + unsigned long ruval;
> + unsigned long ruval2;
> + unsigned long rlval;
> +
> + /* get a consistant pair of upper/lower timebase (no wrap occured) */
> + asm volatile(
> + "loop:\n"
> + "mftbu %0\n"
> + "mftbl %1\n"
> + "mftbu %2\n"
> + "cmpw %0, %2\n"
> + "bne loop"
> + : "=r" (ruval), "=r" (rlval), "=r" (ruval2)
> + );
> +
> + return (((__u64)ruval) << 32) | rlval;
> +}
You should use get_tb() here (see asm-powerpc/time.h).
--
Hollis Blanchard
IBM Linux Technology Center
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