Re: Dual core Athlons and unsynced TSCs

David Lang
2006-01-14T01:09:16Z

On Sat, 14 Jan 2006, Andreas Steinmetz wrote:

> David Lang wrote:
>> On Fri, 13 Jan 2006, Sven-Thorsten Dietrich wrote:
>>
>>> On Fri, 2006-01-13 at 14:05 -0800, David Lang wrote:
>>>
>>>> On Fri, 13 Jan 2006 thockin@hockin.org wrote:
>>>>
>>>>> On Fri, Jan 13, 2006 at 01:18:35PM -0800, David Lang wrote:
>>>>>
>>>>>> Lee, the last time I saw this discussion I thought it was
>>>>>> identified that
>>>>>> the multiple cores (or IIRC the multiple chips in a SMP
>>>>>> motherboard) would
>>>>>> only get out of sync when power management calls were made (hlt or
>>>>>> switching the c-state). IIRC the workaround that was posted then
>>>>>> was to
>>>>>> just disable these in the kernel build.
>>>>>
>>>>>
>>>>> not using 'hlt' when idling means that you spend 10s of Watts more
>>>>> power
>>>>> on mostly idle systems.
>>>>
>>>>
>>>> true, but for people who need better time accruacy then the other
>>>> workaround this may be very acceptable.
>>>>
>>>
>>> 1/4 KW / day for time synchronisation.
>>>
>>> The power company would love that.
>>
>>
>> more precisely 1/4 KW Hour / day
>>
>> $0.01 - $0.02/day (I had to lookup the current rates)
>>
>> they probably won't notice.
>>
>
> Well, wait until there's AMD based dual core x86_64 laptops out there
> (this email being written on a single core x86_64 one). I can already
> see the faces of the unhappy future owners being told "use idle=poll"
> when on battery and anyway going deaf by fan noise.
>
> (/me ducks and runs)

I'm not saying it's the right answer, but it's one of two workarounds
currently available.

idle=poll causes increased power useage

timer source change (mentioned earlier in this thread) limits timer
precision

neither of these are fixes, but by understanding the different costs
people can choose the work around they want to use while waiting for a
better fix.

David Lang

--
There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. And the other way is to make it so complicated that there are no obvious deficiencies.
-- C.A.R. Hoare