On Feb 11, 2014, at 10:01 AM, McAninley, Jason <jmcaninl@xxxxxxxxxx> wrote:
> Thanks for the reply, Bruce.
>
>> Are you using UDP or TCP?
>
> TCP.
>
>> And what do you mean by "maximum packet size"?
>
> I'm generally referring to the Frame size (e.g. 32,626) and/or the TCP packet size (e.g. 32560) - The former being the size of the latter plus the ethernet/IP headers.
>
>> To see if the maximum rsize/wsize is being used you'd need to look for
>> the length of the data in a READ reply or WRITE call.
>
> Right. When I check the contents of a WRITE RPC, I see "Data" length of 32768 (32k).
>
> My understanding is that setting {r,w}size doesn't guarantee that will be the agreed-upon value. Apparently one must check the value in /proc. I have verified this by checking the value of /proc/XXXX/mounts, where XXXX is the pid for nfsv4.0-svc on the client. It is set to a value >32K.
>
>> What actual problem are you trying to solve? (Is your read or write
>> bandwidth lower than you expected?)
>
> I am trying to maximize throughout within a parallel processing cluster. We have GigE connections within our closed network and I would like to ensure we are fully utilizing our bandwidth. Additionally, I find a lot of information online (that is not outdated) suggests various Kernel/OS/NFS settings without giving details for why the settings should be modified.
A closed network introduces the opportunity to use jumbo Ethernet frames. But this assumes your server NICs and switches can support it.
> Upon changing the rsize/wsize, I would have expected to see a change in the packet/payload size, but I do not.
The application itself may play a significant role. If it is writing and flushing, or using O_SYNC, for example, the NFS client may have no choice but to use WRITE operations smaller than wsize.
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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