[petsc-dev] Fwd: Re: [Xlab] slow pagefault on KNC

[Karl Rupp]

Hi,

things are not as severe - just a hardware/configuration problem...

Best regards,
Karli


-------- Original Message --------
Subject: Re: [Xlab] slow pagefault on KNC
Date: Mon, 17 Dec 2012 19:06:53 -0600
From: Kazutomo Yoshii <kazutomo at mcs.anl.gov>
To: xlab at cels.anl.gov <xlab at cels.anl.gov>


This only happens on particular hardware(or maybe configuration).

It's approx 6 usec on normal cards, which is good.

I'm tracking down what is causing this problem.

- kaz

On 12/17/2012 10:48 AM, Kazutomo Yoshii wrote:
> Hi,
>
> I noticed that pagefault is very slow on KNC.  It takes 850 usec
> while it takes ~1 usec on Xeon, so prefaulting 1GB of memory region
> takes 222 sec on KNC.
>
> This may not impact a big app runs for hours and hours, but I guess
> this definitely affects short-lived processes or threads, which might
> make MIC less fascinating.
>
> This could be a hardware problem(need to check Phi), a kernel bug,
> or maybe sage of SMP kernel on many-core.
> If this is the last case, it would be really interesting for me.
>
> Attached a simple page fault benchmark.
>
> - kaz


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