linux-kernel - Re: Please, put 64-bit counter per task and incr.by.one each ctxt switch.

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Date:	Tue, 26 Feb 2008 14:20:44 +0100
From:	"J.C. Pizarro" <jcpiza@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Please, put 64-bit counter per task and incr.by.one each ctxt switch.

On 2008/2/25, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Sun, 24 Feb 2008 14:12:47 +0100 "J.C. Pizarro" <jcpiza@...il.com> wrote:
>
>  > It's statistic, yes, but it's a very important parameter for the CPU-scheduler.
>  > The CPU-scheduler will know the number of context switches of each task
>  >  before of to take a blind decision into infinitum!.
>
>
> We already have these:
>
>         unsigned long nvcsw, nivcsw; /* context switch counts */
>
>  in the task_struct.

1. They use "unsigned long" instead "unsigned long long".
2. They use "= 0;" instead of "= 0ULL";
3. They don't use ++ (incr. by one per ctxt-switch).
4. I don't like the separation of voluntary and involuntary ctxt-switches,
    and i don't understand the utility of this separation.

The tsk->nvcsw & tsk->nivcsw mean different to i had proposed.

It's simple, when calling to function kernel/sched.c:context_switch(..)
to do ++, but they don't do it.

I propose you
1. unsigned long long tsk->ncsw = 0ULL;  and  tsk->ncsw++;
2. unsigned long long tsk->last_registered_ncsw = tsk->ncsw; when it's polling.
3. long tsk->vcsw =  ( tsk->ncsw - tsk->last_registered_ncsw ) / ( t2 - t1 )
/* velocity of task (ctxt-switches per second), (t1 != t2 in seconds
for no zerodiv)
4. long tsk->last_registered_vcsw = tsk->vcsw;
5. long tsk->normalized_vcsw =
       (1 - alpha)*tsk->last_registered_vcsw + alpha*tsk->vcsw; /* 0<alpha<1 */

    Sincerely yours ;)
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