[mkgmap-dev] Re: [PATCH v10] make maps in parallel

Tue May 19 12:21:40 BST 2009

Hi Toby,

> And some performance numbers for you.  First, the baseline run:
> 
> /--------
> | real    14m57.309s
> | user    16m40.606s
> | sys     0m9.813s
> \--------
> 
> Then with --max-jobs:
> 
> /--------
> | real    6m54.229s
> | user    18m14.016s
> | sys     0m13.125s
> \--------
> 
> This is on an Intel Q6600 (a Core2 Quad) @ 2.4GHz with 6GB of RAM.

Thanks for the numbers.

They are similar to what I see on my mega machine (i.e. the realtime
speedup is around x2) with some increase in the user time.

I have plotted real time versus number of cores (aka --max-jobs) and
for the v10 patch the time diminishes as expected as the number of cores
increases. Going from 1 to 4 cores provides a worthwhile speedup but 4-8
doesn't help very much and above 8 makes no difference.

It's interesting to note how machines differ. I have an AMD dual core
job that is only clocked at 1G and it outperforms (when running
parallel mkgmap) a machine that uses a dual core 3GHz Intel pentium 4.
In terms of raw CPU power the Intel machine (a very cheap Acer job) is
actually quite fast but as soon as you try and do anything useful with
it that involves accessing memory it slows right down to a crawl.

Cheers,

Mark