Date: Thu, 10 Mar 2005 20:08:08 -0800
From: Andrew Morton <akpm@osdl.org>
To: Peter Chubb <peterc@gelato.unsw.edu.au>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Microstate Accounting for 2.6.11
Message-Id: <20050310200808.306caf98.akpm@osdl.org>
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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.
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