20100607, 19:40  #12 
I quite division it
"Chris"
Feb 2005
England
31·67 Posts 
Okay, thanks. I'll try it with the 0.75T range I have left to do and see how much memory it uses.

20100607, 19:53  #13  
Jun 2003
2×3^{4}×29 Posts 
Quote:


20100607, 21:26  #14  
I quite division it
"Chris"
Feb 2005
England
81D_{16} Posts 
Quote:
Sieving from 4e4 to 100G is progressing painfully slowly but of course the first bit is always much slower. I think I'll just stop now and run a whole 1T range, now that I know it will easily fit in 485Mb once sieved to 4e4. I'll post the timings here later. The NPG help file states: "NewPGen is happy with lots of k's to sieve  there is nothing to be gained by dividing a range of k's up and sieving each subrange in turn..." So I'm hoping there will be an increase in efficiency. Last fiddled with by Flatlander on 20100607 at 21:29 

20100607, 21:45  #15  
Jun 2003
11132_{8} Posts 
Quote:
Only true when p >= k range (or maybe range/2). Otherwise there is no increase in efficiency, and might even be slower due to memory pressure (Fast Array vs Normal Array mode). 

20100607, 21:48  #16 
I quite division it
"Chris"
Feb 2005
England
31·67 Posts 
Fair enough.

20100611, 22:25  #17 
Jun 2010
10111111_{2} Posts 

20100611, 22:49  #18 
"Dave"
Sep 2005
UK
2×19×73 Posts 
This is in fact the problem with only sieving to p=4e4 in the first stage. It leaves about 32.5 M k's and therefore NewPGen uses normal array mode. I hadn't worked out why it was so slow until I stopped the sieve at p=1e6. When restarted NewPGen switched to fast array mode and the removal rate jumped from 40 k/sec to 280 k/sec, If there is an advantage (yet to be proven), then the first stage needs to sieve to much closer to p=1e6.

20100611, 23:22  #19 
I quite division it
"Chris"
Feb 2005
England
31×67 Posts 
Re. Megabit Twin Sieve
I tried sieving to 10M then again to 100G. The total time was 1020% slower than letting NPG do it automatically. I would seem that indeed the 'sweet spot' is above 1G. Some scribbled timings: Start to 10M took 15hrs 3m (Leaving 6.1M ks.) Started NPG again. (Used fast array, 384Mb ram.) 10M20M took 1hr 24m 20m100m took 4hrs 25m 100m500m took 2hrs 41m 500m100G to 8hrs 33m Total time c. 32hrs compared with c. 2628 hrs (iirc) letting NPG do it automatically. C2Quad Q6700 at stock 2.66GHz. 2Gb ram, NPG memory at maximum 485Mb. Last fiddled with by Flatlander on 20100611 at 23:27 Reason: Clarification. 
20100611, 23:34  #20  
Jun 2003
11132_{8} Posts 
Quote:
I am asking because I am "fairly confident" that I can write a custom sieve that can sieve a range of k's to 1e6 (or even 10e6) much faster than NewPGen can. NewPGen isn't really optimised for the initial sieving. 

20100611, 23:35  #21 
Jun 2003
1001001011010_{2} Posts 

20100611, 23:48  #22  
I quite division it
"Chris"
Feb 2005
England
2077_{10} Posts 
Quote:
Quote:
All figures subject to slight variation as NPG had high priority while 4 x LLRNet with low priority were running in the background. (So I didn't waste any cycles when NPG finished overnight.) 

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