From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gustavo Franco <stratus@legolas.alternex.com.br>
Date: Fri, 16 Apr 2004 02:13:30 +0000
Subject: Re: [Kernel-janitors] [PATCH] - Replaces yield() with
Message-Id: <407F414A.70708@legolas.alternex.com.br>
List-Id: <kernel-janitors.vger.kernel.org>
References: <407C9AEE.5020808@legolas.alternex.com.br>
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To: kernel-janitors@vger.kernel.org

Randy.Dunlap wrote:

>On Tue, 13 Apr 2004 22:59:10 -0300 Gustavo Franco wrote:
>
>| Hi,
>| 
>| I'm new here, and this is my first patch, following the issue described by
>| Matthew Wilcox: "Calling yield() Considered Harmful" on TODO list.
>| 
>| There is no doubt that isn't necessary replace all yield() calls, but i'm
>| planning to check each case on the tree.Comments?
>| 
>| Hope that helps,
>| Gustavo Franco
>| p.s: This e-mail on the "from" is only for ML traffic, my main e-mail is
>| stratus at acm.dot org.
>| 
>| 
>| --- drivers/cdrom/cdu31a.c.orig 2004-04-13 22:43:55.000000000 -0300
>| +++ drivers/cdrom/cdu31a.c      2004-04-13 22:44:17.000000000 -0300
>| @@ -386,7 +386,7 @@ static inline void sony_sleep(void)
>|         unsigned long flags;
>|                                                                                          
>| 
>|         if (cdu31a_irq <= 0) {
>| -               yield();
>| +               schedule_timeout(1);
>|         } else {                /* Interrupt driven */
>| 
>|                 save_flags(flags);
>
>Makes sense, except that the comment above the function bothers me:
>
>/*
> * Wait a little while (used for polling the drive).  If in initialization,
> * setting a timeout doesn't work, so just loop for a while.
> */
>
>I expect that cdu31a_irq <= 0 means "in initializatgion," so is
>using schedule_timeout() safe here?  anyone checked this?
>
>  
>

Good question. Read this bit from comments on the source.

[...]
 * This interface is (unfortunately) a polled interface.  This is
 * because most Sony interfaces are set up with DMA and interrupts
 * disables.  Some (like mine) do not even have the capability to
 * handle interrupts or DMA.  For this reason you will see a lot of
 * the following:
 *
 *   retry_count = jiffies+ SONY_JIFFIES_TIMEOUT;
 *   while (time_before(jiffies, retry_count) && (! <some condition to 
wait for))
 *   {
 *      while (handle_sony_cd_attention())
 *         ;
 *
 *      sony_sleep();
 *   }
 *   if (the condition not met)
 *   {
 *      return an error;
 *   }
 *
 * This ugly hack waits for something to happen, sleeping a little
 * between every try.  it also handles attentions, which are
 * asynchronous events from the drive informing the driver that a disk
 * has been inserted, removed, etc.
[...]

If it's related with initialization why it isn't being called from 
cdu31a_setup() ?
sony_sleep() is called from other functions as described above on the 
comments.


Hope that helps,
Gustavo Franco





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