From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [RFC PATCH] net: add additional lock to qdisc to increase
 enqueue/dequeue fairness
Date: Tue, 23 Mar 2010 22:18:18 +0100
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To: Alexander Duyck <alexander.h.duyck@intel.com>
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Le mardi 23 mars 2010 =C3=A0 21:54 +0100, Eric Dumazet a =C3=A9crit :
> I wonder if ticket spinlocks are not the problem. Maybe we want a
> variant of spinlocks, so that cpu doing transmits can get the lock
> before other cpus...

Something like this portable implementation :

struct spinprio {
	spinlock_t	lock;
	int		highprio_cnt;
};

void spinprio_lock(struct spinprio *l)
{
	while (1) {
		spin_lock(&l->lock);
		if (!l->highprio_cnt)
			break;
		spin_unlock(&l->lock);
		cpu_relax();
	}
}

void spinprio_unlock(struct spinprio *l)
{
	spin_unlock(&l->lock);
}

void spinprio_relock(struct spinprio *l)
{
	l->highprio_cnt =3D 1;
	spin_lock(&l->lock);
	l->highprio_cnt =3D 0;
}

We would have to use spinprio_unlock()/spinprio_relock() in
sch_direct_xmit()