netdev - Re: [RFC] tcp: use order-3 pages in tcp

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Message-ID: <1348247465.2669.766.camel@edumazet-glaptop>
Date:	Fri, 21 Sep 2012 19:11:05 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	rick.jones2@...com, subramanian.vijay@...il.com,
	netdev@...r.kernel.org
Subject: Re: [RFC] tcp: use order-3 pages in tcp_sendmsg()

On Fri, 2012-09-21 at 13:04 -0400, David Miller wrote:

> It's a silly limitation, in net/core/dev.c:
> 
> 	/* Turn on no cache copy if HW is doing checksum */
> 	if (!(dev->flags & IFF_LOOPBACK)) {
> 		dev->hw_features |= NETIF_F_NOCACHE_COPY;
> 		if (dev->features & NETIF_F_ALL_CSUM) {
> 			dev->wanted_features |= NETIF_F_NOCACHE_COPY;
> 			dev->features |= NETIF_F_NOCACHE_COPY;
> 		}
> 	}
> 
> Maybe this is probably better done as:
> 
> 	/* Turn on no cache copy if HW is doing checksum */
> 	dev->hw_features |= NETIF_F_NOCACHE_COPY;
> 	if (!(dev->flags & IFF_LOOPBACK)) {
> 		if (dev->features & NETIF_F_ALL_CSUM) {
> 			dev->wanted_features |= NETIF_F_NOCACHE_COPY;
> 			dev->features |= NETIF_F_NOCACHE_COPY;
> 		}
> 	}
> 
> And then the code matches more closely the comment. :-)

I did a test, and for various combinations (producer/consumer on same
core or not, same cpu or not...) and performance is divided by 2

So I guess we can leave the code as is


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