[Qemu-devel] Re: [PATCH] Autodetect clock_gettime

[Paolo Bonzini]

On 03/15/2011 02:16 PM, Tristan Gingold wrote:
> Some POSIX OSes (such as Darwin) doesn't have clock_gettime.  This patch
> falls back on gettimeofday if clock_gettime is not available.

This may be okay as a stopgap measure, but any sane porting target for 
QEMU should have a monotonic clock.  In fact, Darwin has it.

http://www.wand.net.nz/~smr26/wordpress/2009/01/19/monotonic-time-in-mac-os-x/ 
hints that code such as the following should work and return nanoseconds:

#import <mach/mach_time.h>

    uint64_t t = mach_absolute_time();
    static mach_timebase_info_data_t info;
    if (info.denom == 0) {
        mach_timebase_info(&info);
    }
    return muldiv64(t, info.numer, info.denom);

Paolo