netdev - Re: [RFC PATCH] net: add additional lock to qdisc to increase enqueue/dequeue fairness

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Message-ID: <1269379098.2915.34.camel@edumazet-laptop>
Date:	Tue, 23 Mar 2010 22:18:18 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC PATCH] net: add additional lock to qdisc to increase
 enqueue/dequeue fairness

Le mardi 23 mars 2010 à 21:54 +0100, Eric Dumazet a écrit :
> 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 = 1;
	spin_lock(&l->lock);
	l->highprio_cnt = 0;
}

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



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