[Info-vax] OS implementation languages

[Johnny Billquist]

On 2023-08-31 15:30, Dan Cross wrote:
> In article <215e5a5a-d9b6-40fb-ad94-3ee8e8ad92e8n at googlegroups.com>,
> gah4  <gah4 at u.washington.edu> wrote:
>> On Tuesday, August 29, 2023 at 10:25:31 AM UTC-7, Simon Clubley wrote:
>>   
>> (snip)
>>
>>> 400GB/s ??? Is that all ??? Amateurs!!! :-)
>>
>>> On a more serious note, I wonder what the maximum rate VMS is capable
>>> of emitting data at if it was using the fastest network hardware
>>> available.
>>
>> I am not sure what hardware can do now.
>>
>> Traditionally, Ethernet was much faster than processors, such that the
>> shared media could handle the load.
>>
>> That is less obvious now, but a 400Gb/s network doesn't mean that one host
>> can go that fast.
> 
> 400Gbps is at the high-end of what one can deliver to a single
> system at this point; one or two infiniband cards into a PCIe
> gen4 backplane will get you there.
> 
> This will overwhelm just about any general purpose CPU currently
> on the market, so a lot of overhead is offloaded to accelerator
> hardware on the NIC, but making effective use of _that_ requires
> specialized drivers and cooperation with the host.  As a simple
> example, the NIC may support offloading layer 3 checksum
> calculations, but in order to use that effectively the host
> software has to know about it, configure the hardware to do it,
> and configure itself to avoid repeating the calculations higher
> up in the stack (otherwise, what's the point of offloading?).

Well. It's not that you are so much overloading the CPU as the bus. It's 
a huge bottleneck to move data anywhere. So yes, offloading as much as 
possible out to where the data is already passing by anyway is a big win.

I haven't checked, but I would hope that VMS can also make use of things 
like checksum offloading. Pretty much any other OS can these days.

> This also implies that, "throw more hardware at it!" is only
> part of a possible solution to a performance problem: if the
> software isn't similarly modified to take advantage of the
> capabilities of that hardware, you may not see much in terms of
> actual gains.

Certainly. If you throw hardware at a problem, and then don't use the 
hardware, you didn't gain anything.

	Johnny