[Info-vax] State of the Port - July 2017

[Stephen Hoffman]

On 2017-07-20 21:40:53 +0000, Jan-Erik Soderholm said:

> Den 2017-07-20 kl. 23:37, skrev Stephen Hoffman:
>> On 2017-07-18 21:27:18 +0000, Scott Dorsey said:
>> 
>>> Infiniband is designed for low latency.  If what you need is the lowest 
>>> possible latency, Infiniband is likely a big win over ethernet.  If you 
>>> need fastest throughput for bulk transfers, ethernet is likely a big 
>>> win for you instead.
>> 
>> Ethernet is reaching well up into the same market Infiniband is aimed 
>> at, and VSI is going to want to and need to go after better Ethernet 
>> support to start with as it's far more broadly applicable.   Once the 
>> x86-64 port is out and VSI has 40 GbE and 100 GbE and other related 
>> support available,...
> 
> Doesn't that come "for free" if you're running under a VM?

We don't yet know what VSI will be providing for their virtual machine 
support; which particular virtual machines will be supported and what 
features.   If the virtual machine and the I/O path involves 
virtualized device support, then OpenVMS will need drivers for the 
virtual device and network I/O will incur some overhead going through 
the host driver layer and the host drivers will deal with the specifics 
of the particiular device.   This is simpler, but there's more overhead 
and particularly if there's a lot of I/O buffer copying involved.   If 
the I/O device is accessed directly from the guest operating system 
bypassing the host operating system or the host VM, then there'll be 
device-specific drivers needed in OpenVMS.    For VM-related details 
here, see discussions of device virtualization and paravirtualization, 
among others.   In either approach, system performance around 100 GbE 
or Infiniband involves a whole lot of interrupts, and those have to be 
handled expeditiously for the hardware to be used effectively.  Also 
see the TCP Offload Engine (TOE) discussions and the details of what 
Infiniband provides and how, as both of those seek to provide faster 
and lower-latency networking.

> You get whatever netork support that the VM supports, not?

We get what VSI supports, or maybe what a third-party provides with 
their hardware.




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