Re: [RFC][PATCH] Runtime switching of the idle function [take 2]

[Andrew Morton <akpm@osdl.org>]

Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Mon, 2005-11-28 at 19:02 -0800, Andrew Morton wrote:
>  > Steven Rostedt <rostedt@goodmis.org> wrote:
>  > >
>  > > This patch creates a directory in /sys/kernel called idle.
>  > >
>  > 
>  > At no point do you appear to explain _why_ the kernel needs this feature?
> 
>  Sorry about that.  This originally came up when we had problems with the
>  AMD64 x2 in the -rt patch.  It was noted that the TSCs would get very
>  far out of sync and cause problems.

Unsynced TSCs are rare, but they happen.  I guess even if we were to resync
them, these measurements would screw up.


> The way to solve this was to set
>  idle=poll.  The original patch I sent was to allow the user to change to
>  idle=poll dynamically.  This way they could switch to the poll_idle and
>  run there tests (requiring tsc not to drift) and then switch back to the
>  default idle to save on electricity.

Use gettimeofday()?

If it's just for some sort of instrumentation, run NR_CPUS instances of a
niced-down busyloop, pin each one to a different CPU?  That way the idle
function doesn't get called at all..