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

[Tristan Gingold]

On Mar 15, 2011, at 2:58 PM, Paolo Bonzini wrote:

> On 03/15/2011 02:47 PM, Tristan Gingold wrote:
>> 
>> On Mar 15, 2011, at 2:34 PM, Paolo Bonzini wrote:
>> 
>>> 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.
>> 
>> Yes mach primitives could be used.  But why isn't a monotonic clock used on 
>> Linux ?  According to man, CLOCK_MONOTONIC is monotonic
>> while CLOCK_REALTIME isn't.
> 
> /me rereads the patch
> 
> Unfortunately, pthread timed wait/lock functions are documented to use the 
> realtime clock by default.  Using pthread_condattr_setclock is probably not 
> portable enough, and anyway there is no such function for mutexes so we're 
> stuck with CLOCK_REALTIME.  What you're patching is fine, but those functions 
> might actually go away soon as they're not supported on Win32.

Fine.

> So, in addition to what you've done, you should probably use those Mach 
> primitives in qemu-timer.h.

Yes.  But note that the first aim of this patch is to make qemu compiling again 
on Darwin.

Tristan.