linux-kernel - Re: [PATCH net-next] tuntap: introduce tx skb ring

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Date:	Wed, 18 May 2016 11:21:59 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Jason Wang <jasowang@...hat.com>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] tuntap: introduce tx skb ring

On Wed, May 18, 2016 at 10:16:31AM +0200, Jesper Dangaard Brouer wrote:
> 
> On Tue, 17 May 2016 09:38:37 +0800 Jason Wang <jasowang@...hat.com> wrote:
> 
> > >> And if tx_queue_length is not power of 2,
> > >> we probably need modulus to calculate the capacity.  
> > > Is that really that important for speed?  
> > 
> > Not sure, I can test.
> 
> In my experience, yes, adding a modulus does affect performance.

How about simple
	if (unlikely(++idx > size))
		idx = 0;


> > 
> > Right, this sounds a good solution.
> 
> Good idea.

I'm not that sure - it's clearly wasting memory.

> -- 
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   Author of http://www.iptv-analyzer.org
>   LinkedIn: http://www.linkedin.com/in/brouer