Re: [PATCH 1/3] include files for kvmclock

Gerd Hoffmann
2007-11-09T08:38:21Z

> +/*
> + * Guest has page alignment and padding requirements. At the host, it will
> + * only lead to wasted space at the vcpu struct. For this reason, the struct
> + * is not anonymous
> + */
> +union kvm_hv_clock {
> + struct kvm_hv_clock_s {
> + u64 tsc_mult;
> + u64 now_ns;
> + /* That's the wall clock, not the water closet */
> + u64 wc_sec;
> + u64 last_tsc;
> + /* At first, we could use the tsc value as a marker, but Jeremy
> + * well noted that it will cause us locking problems in 32-bit
> + * sys, so we have a special version field */
> + u32 version;
> + } fields;
> + char page_align[PAGE_SIZE];
> +};

What is the point in using a whole page per vcpu? You probably don't
want struct kvm_hv_clock_s cross a page border. Is that the only reason
or are there other constrains too?

As the kvm clock looks quite simliar to what xen does, how about making
the structs binary-compatible or simply reuse the xen version (struct
vcpu_time_info in xen/interface/xen.h)?

cheers,
Gerd