Re: [Qemu-devel] [PATCH 1/3] use nanoseconds everywhere for timeout computation

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Jan 31, 2011 at 04:17:52PM -0600, Anthony Liguori wrote:
> On 01/31/2011 03:51 PM, Paolo Bonzini wrote:
>> Suggested by Aurelien Jarno.
>>
>> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
>>    
>
> Something I've found is that we have a lot of bugs that are the result  
> of unit conversions when the unit can't be mapped directly to base 10.
>
> This happens in both the PIT and RTC and probably every other fixed bus  
> speed based clock we support.
>
> I think it would be better to have a Unit argument to qemu_get_clock to  
> specify the desired units.  That way, we could request NS as the time  
> unit or something like PC_FREQ0 which would map to the bus speed of the 
> PIT.

It's more or less what is already done with the two versions of the
functions, qemu_get_clock() which can return different unit depending on
what you ask (and in my opinion should simply disappear because it's the
best way to have bugs), and qemu_get_clock_ns() that always return it in
nanoseconds. What you suggests is a generalization of this second
function to different units than ns.

That's an option, but we should pay attention that given we work in
integer, a conversion decrease the precision, so it should usually be 
done at the last moment to keep the precision correct (assuming ns is
precise enough, which I guess is true).

In any case I think this patch series should be applied as it fixes a
real bug. It's already a step in the right direction, as it removes
useless conversions, as all the involved functions use ns in fine.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net