Re: Interacting with coherent memory on external devices

From: Paul E. McKenney
Date: Fri Apr 24 2015 - 10:14:17 EST

On Fri, Apr 24, 2015 at 09:01:47AM -0500, Christoph Lameter wrote:
> On Thu, 23 Apr 2015, Paul E. McKenney wrote:
> > > As far as I know Jerome is talkeing about HPC loads and high performance
> > > GPU processing. This is the same use case.
> >
> > The difference is sensitivity to latency. You have latency-sensitive
> > HPC workloads, and Jerome is talking about HPC workloads that need
> > high throughput, but are insensitive to latency.
> Those are correlated.

In some cases, yes. But are you -really- claiming that -all- HPC
workloads are highly sensitive to latency? That would be quite a claim!

> > > What you are proposing for High Performacne Computing is reducing the
> > > performance these guys trying to get. You cannot sell someone a Volkswagen
> > > if he needs the Ferrari.
> >
> > You do need the low-latency Ferrari. But others are best served by a
> > high-throughput freight train.
> The problem is that they want to run 2000 trains at the same time
> and they all must arrive at the destination before they can be send on
> their next trip. 1999 trains will be sitting idle because they need
> to wait of the one train that was delayed. This reduces the troughput.
> People really would like all 2000 trains to arrive on schedule so that
> they get more performance.

Yes, there is some portion of the market that needs both high throughput
and highly predictable latencies. You are claiming that the -entire- HPC
market has this sort of requirement? Again, this would be quite a claim!

Thanx, Paul

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