Re: ++idlepoll

From: Francesco Pietra (
Date: Mon Feb 06 2017 - 02:37:33 CST


what about

"nvidia-smi -pm 1"

that I command with a single node linux box before launching namd2 ...

Also, is "+idlepoll" equivalent to "++idlepoll"?


francesco pietra

On Mon, Feb 6, 2017 at 9:15 AM, Norman Geist <
> wrote:

> In simple words:
> In distributed parallel implementations, two or more endpoints that share
> some kind of network connection exchange messages. In the case of GPU
> acceleration this network is the PCIE bus and the endpoints are the CPU and
> the GPU. The CPU puts work to the GPU and must wait for the GPU to return
> back the result. Since the CPU can’t know when the GPU will be finished, it
> must frequently ask the GPU if it has finished, this is called polling.
> Such polling without a wait time in-between is very CPU intensive
> (++idlepoll), but with a wait time of N, there’s always a chance of getting
> the results N time too late, so this would waste time and increase latency.
> Therefore using ++idlepoll is absolutely recommended, and even forced for
> GPU runs.
> Norman Geist
> *Von:* [] *Im
> Auftrag von *Zeki Zeybek
> *Gesendet:* Montag, 6. Februar 2017 08:21
> *An:*
> *Betreff:* namd-l: ++idlepoll
> Hi!
> I was just wondering what is the rationale behind adding this command in
> order to run a simulation on GPU. Simply I did not really understand what
> the statement `you should add +idlepoll to the command line in order to
> poll the GPU for results rather than sleeping while idle` means. Sorry for
> my ignorance on the matter. I would appreciate any sort of detailed info on
> the matter. Thank you in advance

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