Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id <S131387AbRCSJrZ>; Mon, 19 Mar 2001 04:47:25 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org
	id <S131376AbRCSJrO>; Mon, 19 Mar 2001 04:47:14 -0500
Received: from mail.zmailer.org ([194.252.70.162]:29965 "EHLO zmailer.org")
	by vger.kernel.org with ESMTP id <S131385AbRCSJrJ>;
	Mon, 19 Mar 2001 04:47:09 -0500
Date: Mon, 19 Mar 2001 11:46:15 +0200
From: Matti Aarnio <matti.aarnio@zmailer.org>
To: watermodem <aquamodem@ameritech.net>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Jiffy question and sound.
Message-ID: <20010319114615.E23336@mea-ext.zmailer.org>
In-Reply-To: <3AB5A53F.F8B0373B@ameritech.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <3AB5A53F.F8B0373B@ameritech.net>; from aquamodem@ameritech.net on Mon, Mar 19, 2001 at 12:20:47AM -0600
Sender: linux-kernel-owner@vger.kernel.org
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Mar 19, 2001 at 12:20:47AM -0600, watermodem wrote:
> With the 2.4.0 kernel the loops_per_sec field was replaced (for i386)
> with current_cpu_data.loops_per_jiffy.
...
> #define LOOPS_PER_SEC current_cpu_data.loops_per_jiffy * 100

  The intention was to accomodate systems with faster than 2 GHz clock
  at which the LOOPS_PER_SEC counter spins around a bit too fast..
  ('signed long' at i386 handles 0..2G just fine, then it thinks the sign
   got inverted..  'unsigned long' works fine until 4 GHz processors.)

  Why does the ALSA need  LOOPS_PER_SEC ?
  Is it doing timing by busy-looping ?

> Now compiling the same  ALSA modules with 2.4.2 this problem happens
> much quicker and you don't need any other activity.  In fact it is hard
> to play more than half a song.  (MP3)
> It doesn't matter if what set of music players or tools I use the
> problem is quite visible.
> 
> When I boot back to the original 2.2.x kernel everything is perfect.   
> 
> So I guess I have a few questions here.
>  1)   Is a jiffy 100th of a second or is it smaller  (so my loop count
> is starving things.) (10ms) ?

	"HZ" is the answer.  E.g. Alpha has HZ=1024, while i386 has HZ=100
	Nearly all architectures have different values based on what some
	other UNIX uses at given system.

>  2)   Why is it so much worse in 2.4.2 than 2.4.0?
>  3)   Any other "gotch's" that are important to watch for when moving
> 2.2.x drivers to 2.4.x?

	The FAQ may have some pointers to "porting drivers to 2.4" documents.

> Thanks....
> Watermodem
> -
> Please read the FAQ at  http://www.tux.org/lkml/

/Matti Aarnio
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/