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From: Con Kolivas <kernel@kolivas.org>
To: Timothy Miller <miller@techsource.com>
Cc: linux kernel mailing list <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>,
	gaxt <gaxt@rogers.com>, Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH] O16int for interactivity
Date: Sat, 16 Aug 2003 12:31:50 +1000	[thread overview]
Message-ID: <200308161231.50661.kernel@kolivas.org> (raw)
In-Reply-To: <3F3D25D0.7010701@techsource.com>

On Sat, 16 Aug 2003 04:26, Timothy Miller wrote:
> Con Kolivas wrote:
> > Preemption of tasks at the same level with twice as much timeslice has
> > been dropped as this is not necessary with timeslice granularity (may
> > improve performance of cpu intensive tasks).
>
> Does this situation happen where two tasks at different nice levels have
> dynamic priority adjustments which make them effectively have the same
> priority?

Yes it does. Preemption and order of scheduling is determined entirely by the 
dynamic priority.

> > Preemption of user tasks is limited to those in the interactive range;
> > cpu intensive non interactive tasks can run out their full timeslice (may
> > also improve cpu intensive performance)
>
> What can cause preemption of a task that has not used up its timeslice?

Any task of better (dynamic) priority will preempt it.

>   I assume a device interrupt could do this, but... there's a question I
> asked earlier which I haven't read the answer to yet, so I'm going to
> guess:
>
> A hardware timer interrupt happens at timeslice granularity.  If the
> interrupt occurs, but the timeslice is not expired, then NORMALLY, the
> ISR would just return right back to the running task, but sometimes, it
> might decided to end the timeslice early and run some other task.
>
> Right?

No, the timeslice granularity is a hard cut off where a task gets rescheduled 
and put at the back of the queue again. If there is no other task of equal or 
better priority it will just start again.

> So, what might cause the scheduler to decide to preempt a task which has
> not used up its timeslice?

Better dynamic priority.

Con


  parent reply	other threads:[~2003-08-16  2:25 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-08-15 15:49 [PATCH] O16int for interactivity Con Kolivas
2003-08-15 18:26 ` Timothy Miller
2003-08-15 18:45   ` Richard B. Johnson
2003-08-16  2:31   ` Con Kolivas [this message]
2003-08-18 15:46     ` Timothy Miller
2003-08-18 15:43       ` Nick Piggin
2003-08-18 19:48         ` Timothy Miller
2003-08-18 22:46           ` Nick Piggin
2003-08-15 19:00 ` Felipe Alfaro Solana
2003-08-16  2:14   ` [PATCH]O16.1int was " Con Kolivas
2003-08-15 21:01 ` Mike Fedyk
2003-08-15 23:03 ` Scheduler activations (IIRC) question Jamie Lokier
2003-08-15 23:54   ` Mike Fedyk
2003-08-16  0:54     ` Jamie Lokier
2003-08-16  6:14       ` Mike Galbraith
2003-08-16 14:18         ` Jamie Lokier
2003-08-17  5:51           ` Mike Galbraith
2003-08-17  6:55             ` Jamie Lokier
2003-08-17  7:05               ` Nick Piggin
2003-08-17  8:34               ` Mike Galbraith
2003-08-17 17:12                 ` Jamie Lokier
2003-08-17 17:15                   ` Arjan van de Ven
2003-08-17 18:26                     ` Jamie Lokier
2003-08-17 18:27                   ` Mike Galbraith
2003-08-17 18:29                     ` Jamie Lokier
2003-08-17 18:46                     ` Jamie Lokier
2003-08-16 20:54         ` Ingo Oeser
2003-08-16 21:39           ` Jamie Lokier
     [not found]             ` <20030817144203.J670@nightmaster.csn.tu-chemnitz.de>
2003-08-17 20:02               ` Jamie Lokier
2003-08-18  0:23                 ` William Lee Irwin III
2003-08-18 10:38                 ` Ingo Oeser
2003-08-18 13:09                   ` Jamie Lokier
2003-08-16  7:01 ` [PATCH] O16int for interactivity Con Kolivas
2003-08-18 10:08 ` Apurva Mehta
2003-08-18 10:30   ` Con Kolivas
2003-08-18 12:13     ` Apurva Mehta
2003-08-15 20:50 Voluspa

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