I actually don't think there's any problem with parallel initialization. It
could well be happening, but shouldn't be causing a dramatic slow down.
I would like to send you a short video clip tomorrow to illustrate what I am
seeing on my machine. It is possible there is something machine dependent? We
are using a new Skylake machine.
-- Dave W (sent from my phone, so please excuse brevity, speak-o's, and
swype-o's)
On July 12, 2016 6:41:37 PM EDT, Elliot Ronaghan <[email protected]> wrote:
>>It looks like the
>>
>>-sparallelInitElts=false
>>
>>setting restored our performance to what we got with 1.11.
>Surprisingly (to
>>me), without this flag, the code seems to be using multicore execution
>of the
>>loops I've written, as well as perhaps the array initialization (at
>least,
>>that's what it looks like when I watch htop as I run it, and all 4
>cores run at
>>100% right up until it quits 12 seconds after starting). That would
>probably
>>explain the terrible performance, as the untiled loop nest would
>probably cause
>>terrible contention for cache lines if run concurrently.
>
>That flag only impacts array initialization. Your for-loops will still
>run
>serially (Chapel, very intentionally, does not auto-parallelize
>anything.)
>When I run, I see a spike for all cores during array initialization,
>then
>just one core busy for the rest of the program.
>
>>I'm attaching our code, but my question may now just be: how to I
>prevent
>>concurrent execution (and the answer may be, with the flag above).
>
>For now, I'd just use -sparallelInitElts=false. Currently there's no
>way to
>squash the default array initialization, but we're working on that. In
>the
>future you should be able to get serial array init by doing something
>like:
>
> // replace default init with manual serial init
> var m: [MatrixD] int = for i in MatrixD do 0;
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