Re: Help with NFS over 10GbE performance - possible NFS client to TCP bottleneck

[Jeff Wright <jeff.wright@oracle.com>]

Andy,

We did not check the RPC statistics on the client, but on the target the 
queue is nearly empty.  What is the command to check to see the RPC 
backlog on the Linux client?

Thanks,

Jeff

On 06/13/12 09:08, Andy Adamson wrote:
> Chuck recently brought this to my attention:
>
> Have you tried looking at the RPC statistics average backlog queue
> length in mountstats? The backlog queue gets filled with NFS requests
> that do not get an RPC slot.
>
> I assume that jumbo frames are turned on throughout the connection.
>
> I would try some iperf runs.  This will check the throughput of the
> memory<->  network<->  memory path and provide an upper bound on what
> to expect from NFS as well as displaying the MTU to check for jumbo
> frame compliance.
>
> I would then try some iozone tests, including the O_DIRECT tests. This
> will give some more data on the issue by separating throughput from
> the application specifics.
>
> -->Andy
>
> On Tue, May 22, 2012 at 12:21 PM, Jeff Wright<jeff.wright@oracle.com>  wrote:
>> Team,
>>
>> I am working on a team implementing a configuration with an OEL kernel
>> (2.6.32-300.3.1.el6uek.x86_64) and kernel NFS accessing an NFS server over
>> 10GbE a Solaris 10.  We are trying to resolve what appears to be a
>> bottleneck between the Linux kernel NFS client and the TCP stack.
>>   Specifically, the TCP send queue on the Linux client is empty (save a
>> couple of bursts) when we are running write I/O from the file system, the
>> TCP receive queue on the Solaris 10 NFS server is empty, and the RPC pending
>> request queue on the Solaris 10 NFS server is zero.   If we dial the network
>> to 1GbE we get a nice deep TCP send queue on the client, which is the
>> bottleneck I was hoping to get to with 10GbE.  At this point, we am pretty
>> sure the S10 NFS server can run to at least 1000 MBPS.
>>
>> So far, we have implemented the following Linux kernel tunes:
>>
>> sunrpc.tcp_slot_table_entries = 128
>> net.core.rmem_default = 4194304
>> net.core.wmem_default = 4194304
>> net.core.rmem_max = 4194304
>> net.core.wmem_max = 4194304
>> net.ipv4.tcp_rmem = 4096 1048576 4194304
>> net.ipv4.tcp_wmem = 4096 1048576 4194304
>> net.ipv4.tcp_timestamps = 0
>> net.ipv4.tcp_syncookies = 1
>> net.core.netdev_max_backlog = 300000
>>
>> In addition, we am running jumbo frames on the 10GbE NIC and we have
>> cpuspeed and irqbalance disabled (no noticeable changes when we did this).
>>   The mount options on the client side are as follows:
>>
>> 192.168.44.51:/export/share on /export/share type nfs
>> (rw,nointr,bg,hard,rsize=1048576,wsize=1048576,proto=tcp,vers=3,addr=192.168.44.51)
>>
>> In this configuration we get about 330 MBPS of write throughput with 16
>> pending stable (open with O_DIRECT) synchronous (no kernel aio in the I/O
>> application) writes.  If we scale beyond 16 pending I/O response time
>> increases but throughput remains fixed.  It feels like there is a problem
>> with getting more than 16 pending I/O out to TCP, but we can't tell for sure
>> based on our observations so far.  We did notice that tuning the wsize down
>> to 32kB increased throughput to 400 MBPS, but we could not identify the root
>> cause of this change.
>>
>> Please let us know if you have any suggestions for either diagnosing the
>> bottleneck more accurately or relieving the bottleneck.  Thank you in
>> advance.
>>
>> Sincerely,
>>
>> Jeff
>> --
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