Re: Microstate Accounting for 2.6.11

[Andrew Morton <akpm@osdl.org>]

Peter Chubb <peterc@gelato.unsw.edu.au> wrote:
>
>  Timing data on threads at present is pretty crude:  when the timer
>  interrupt occurs, a tick is added to either system time or user time
>  for the currently running thread.  Thus in an unpacthed kernel one can
>  distinguish three timed states:  On-cpu in userspace, on-cpu in system
>  space, and not running.
> 
>  The actual number of states is much larger.  A thread can be on a
>  runqueue or  the expired queue (i.e., ready to run but not running),
>  sleeping on a semaphore or on a futex, having its time stolen to
>  service an interrupt, etc., etc.
> 
>  This patch adds timers per-state to each struct task_struct, so that
>  time in all these states can be tracked.  This patch contains the core
>  code do the timing, and to initialise the timers.  Subsequent patches
>  enable the code (by adding Kconfig options) and add hooks to track
>  state changes.

Why does the kernel need this feature?

Have you any numbers on the overhead?

The preempt_disable() in sys_msa() seems odd.