Re: Dual core Athlons and unsynced TSCs

From: David Lang
Date: Fri Jan 13 2006 - 20:07:48 EST


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@xxxxxxxxxx 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

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