Hi Dirk,
On 2012-06-19 Dirk Zimoch wrote:
>
> I am testing the performance of array parsing with StreamDevice on a
> Linux system. I am reading strings like "3.1415,3.1415,...\n" into a
> waveform record with FTVL=DOUBLE. The input is via TCP from localhost.
>
> I found a very strange duration/size relationship:
> size 1 duration: 423 time/element: 423.0
> size 2 duration: 234 time/element: 117.0
...
> size 256 duration: 397 time/element: 1.6
> size 512 duration: 552 time/element: 1.1
> size 1024 duration: 40023 time/element: 39.1
> size 2048 duration: 41450 time/element: 20.2
...
> size 524288 duration: 275591 time/element: 0.5
> size 1048576 duration: 518404 time/element: 0.5
>
> All times are in 1e-6 seconds. Time is measured on the server. The clock
> starts before sending the string and stops after the waveform sends back
> an acknowledge.
>
> Protocol: {in "%f"; out "%(NORD)d";}
>
> I understand that for small arrays, the time is dominated by overhead
> and stays more or less constant.
>
> But does anyone have an idea why is there this strange performance drop
> for sizes between 1024 and 4096 elements?
I would second Martin Konrad's cache suggestion, your string data above takes
up 7 characters per element and the double version is 8 bytes per element, so
with 512 elements they each fit into a 4KB MMU page (or straddle two pages).
When you double the number of elements you need 4 pages to store it all, and
that may be where you run out of cache. Try setting FTVL=FLOAT and see if the
break moves upwards at all (you might need to measure at size=768 to detect a
change though). If that doesn't make any difference it could also be a effect
on the machine at the other end of the TCP socket.
- Andrew
--
Never interrupt your enemy when he is making a mistake.
-- Napoleon Bonaparte
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