linux-kernel - Re: [PATCH 2.6.20-rc4 1/4] futex priority based wakeup

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Message-Id: <1168445501.22579.7.camel@imap.mvista.com>
Date:	Wed, 10 Jan 2007 08:11:41 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Pierre Peiffer <pierre.peiffer@...l.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Jean-Pierre Dion <jean-pierre.dion@...l.net>,
	Ingo Molnar <mingo@...e.hu>,
	Ulrich Drepper <drepper@...hat.com>,
	Jakub Jelinek <jakub@...hat.com>,
	Darren Hart <dvhltc@...ibm.com>,
	Sébastien Dugué <sebastien.dugue@...l.net>
Subject: Re: [PATCH 2.6.20-rc4 1/4] futex priority based wakeup

On Tue, 2007-01-09 at 17:16 +0100, Pierre Peiffer wrote:
> @@ -1358,7 +1366,7 @@ static int futex_unlock_pi(u32 __user *u
>         struct futex_hash_bucket *hb;
>         struct futex_q *this, *next;
>         u32 uval;
> -       struct list_head *head;
> +       struct plist_head *head;
>         union futex_key key;
>         int ret, attempt = 0;
> 
> @@ -1409,7 +1417,7 @@ retry_locked:
>          */
>         head = &hb->chain;
> 
> -       list_for_each_entry_safe(this, next, head, list) {
> +       plist_for_each_entry_safe(this, next, head, list) {
>                 if (!match_futex (&this->key, &key))
>                         continue;
>                 ret = wake_futex_pi(uaddr, uval, this);


Is this really necessary? The rtmutex will priority sort the waiters
when you enable priority inheritance. Inside the wake_futex_pi() it
actually just pulls the new owner off another plist inside the the
rtmutex structure.

Daniel

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