netdev - Re: [RFC PATCH] Regression in linux 2.6.32 virtio

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Date:	Wed, 16 Dec 2009 09:42:41 -0800
From:	Sridhar Samudrala <sri@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, mst@...hat.com,
	netdev@...r.kernel.org
Subject: Re: [RFC PATCH] Regression in linux 2.6.32 virtio_net seen with
 vhost-net

On Wed, 2009-12-16 at 13:11 +1030, Rusty Russell wrote:
> Sridhar, if you simply remove the dev_warn() does that restore some
> performance?  I'll work on a proper fix for 2.6.33 now.

Here is the comparision of a 60sec TCP STREAM test from 2.6.31.6 and 2.6.32 guests
to a 2.6.32 host with vhost-net patches.
Removing the dev_warn() in 2.6.32 doesn't make any significant difference
in throughput. I think the requeues are the main cause for the regression.
Will try your xmit NAPI patch.

linux-2.6.32
------------
$ ./netperf -c -C -H 192.168.122.1 -t TCP_STREAM  -l60
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.122.1 (192.168.122.1) port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB

 87380  16384  16384    60.03      3279.98   81.48    77.79    2.035   3.885  
$ tc -s qdisc show dev eth0
qdisc pfifo_fast 0: root refcnt 2 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
 Sent 24708777531 bytes 1469482 pkt (dropped 0, overlimits 0 requeues 283575) 
 rate 0bit 0pps backlog 0b 0p requeues 283575 
$ ip -s link show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 54:52:00:35:e3:74 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    97000940   1469585  0       0       0       0      
    TX: bytes  packets  errors  dropped carrier collsns 
    3233946817 1469533  0       0       0       0      

linux-2.6.31.6
--------------
$ ./netperf -c -C -H 192.168.122.1 -t TCP_STREAM -l60
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.122.1 (192.168.122.1) port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB

 87380  16384  16384    60.03      8038.48   69.44    71.02    0.708   1.448  
$ tc -s qdisc show dev eth0
qdisc pfifo_fast 0: root bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
 Sent 60378698117 bytes 937388 pkt (dropped 0, overlimits 0 requeues 61) 
 rate 0bit 0pps backlog 0b 0p requeues 61 
$ ip -s link show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 54:52:00:35:e3:73 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    54702188   828655   0       0       0       0      
    TX: bytes  packets  errors  dropped carrier collsns 
    248753779  937399   0       7       0       0     


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