netdev - Re: [PATCH] xen/netfront: improve truesize tracking

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Date:	Mon, 7 Jan 2013 14:22:45 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Sander Eikelenboom <linux@...elenboom.it>
CC:	Rick Jones <rick.jones2@...com>,
	Eric Dumazet <erdnetdev@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	annie li <annie.li@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH] xen/netfront: improve truesize tracking

On Mon, 2013-01-07 at 14:11 +0000, Sander Eikelenboom wrote:
> Monday, January 7, 2013, 2:41:03 PM, you wrote:
> 
> > On Thu, 2013-01-03 at 20:40 +0000, Sander Eikelenboom wrote:
> >> Friday, December 21, 2012, 7:33:43 PM, you wrote:
> >> 
> >> > I'm guessing that trusize checks matter more on the "inbound" path than 
> >> > the outbound path?  If that is indeed the case, then instead of, or in 
> >> > addition to using the -s option to set the local (netperf side) socket 
> >> > buffer size, you should use a -S option to set the remote (netserver 
> >> > side) socket buffer size.
> >> 
> >> > happy benchmarking,
> >> 
> >> > rick jones
> >> 
> >> 
> >> OK, ran them with -S as well:
> 
> > Are these all from domU -> dom0 ? Did you try traffic going the other
> > way?
> 
> Yes running netperf in domU and netserver in dom0, but i must say i'm far from a netperf expert.
> So i don't even know for sure if the tests i ran give a good picture.
> 
> >> "current" is with netfront as is        (skb->truesize += skb->data_len - RX_COPY_THRESHOLD;)
> >> "patched" is with IanC's latest patch   (skb->truesize += PAGE_SIZE * skb_shinfo(skb)->nr_frags;)
> 
> skb->>truesize += skb->data_len - NETFRONT_SKB_CB(skb)->pull_to; is
> > probably more interesting to compare against since we know the current
> > one is buggy.
> 
> Will see if i can run against that as well, although i thought Eric
> said to prefer the "skb->truesize += PAGE_SIZE *
> skb_shinfo(skb)->nr_frags;"

Right, I meant to compare "PAGE_SIZE * skb_shinfo(skb)->nr_frags" vs
"skb->data_len - NETFRONT_SKB_CB(skb)->pull_to". TBH I trust Eric so I'm
inclined to just go with what he suggests.

Ian.

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