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

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Date:	Mon, 7 Jan 2013 13:41:03 +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 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?

> "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.

These number generally look good, largely +/- 1%, often in favour of the
updated code but these two stand out as worrying:

> TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.1.1 (192.168.1.1) port 0 AF_INET : +/-2.500% @ 95% conf.  : demo
>         Recv   Send    Send
>         Socket Socket  Message  Elapsed
>         Size   Size    Size     Time     Throughput
>         bytes  bytes   bytes    secs.    KBytes/sec
> 
> current 18000  16384   1432    60.00    37559.94
> patched 18000  16384   1432    60.00    40630.66
> 
> TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.1.1 (192.168.1.1) port 0 AF_INET : +/-2.500% @ 95% conf.  : demo
>         Recv   Send    Send
>         Socket Socket  Message  Elapsed
>         Size   Size    Size     Time     Throughput
>         bytes  bytes   bytes    secs.    KBytes/sec
> 
> current 28000  16384  16384    60.00    103766.68
> patched 28000  16384  16384    60.00    93277.98

That's at least a 10% slow down in both cases.

> UDP UNIDIRECTIONAL SEND TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.1.1 (192.168.1.1) port 0 AF_INET : +/-2.500% @ 95% conf.  : demo
>         Socket  Message  Elapsed      Messages
>         Size    Size     Time         Okay Errors   Throughput
>         bytes   bytes    secs            #      #   KBytes/sec
> 
> current 212992   65507   60.00      252586      0    269305.73
> current   2280           60.00      229371           244553.96
> patched 212992   65507   60.00      256209      0    273168.32
> patched   2280           60.00      201670           215019.54

The recv numbers here aren't too pleasing either.

However, given that this fixes a real issue which people are seeing I'd
be inclined to go with it, at least for now.

Ian.

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