mersenneforum.org  

Go Back   mersenneforum.org > Great Internet Mersenne Prime Search > Hardware

Reply
 
Thread Tools
Old 2005-10-21, 23:48   #1
Longshot
 
Mar 2004
Somewhere downrange

2×7 Posts
Default L2 cache question

Does 512 of L2 cache offer better performance in LL testing over 256 L2 at the same processor speed?
Longshot is offline   Reply With Quote
Old 2005-10-22, 02:59   #2
Prime95
P90 years forever!
 
Prime95's Avatar
 
Aug 2002
Yeehaw, FL

7,013 Posts
Default

Yes
Prime95 is offline   Reply With Quote
Old 2005-10-22, 19:17   #3
Peter Nelson
 
Peter Nelson's Avatar
 
Oct 2004

232 Posts
Default

Quote:
Originally Posted by Prime95
Yes
Am I right in thinking this can be generalised to larger sizes also?

1024 faster than 512

2048 faster than 1024.

And is 2048 the largest cache size currently optimised for?

So eg when machine with 4096 cache is available, the software current client does not yet take advantage and will use code/behaviour as in 2048?
Peter Nelson is offline   Reply With Quote
Old 2005-10-22, 19:52   #4
ColdFury
 
ColdFury's Avatar
 
Aug 2002

26×5 Posts
Default

Quote:
Am I right in thinking this can be generalised to larger sizes also?
Everything else being equal, yes, but increasing the side of caches can cause other side-effects (like increasing cache latency) which may hurt performance. With Prime95 its generally a win though.
ColdFury is offline   Reply With Quote
Old 2005-10-22, 19:56   #5
Prime95
P90 years forever!
 
Prime95's Avatar
 
Aug 2002
Yeehaw, FL

7,013 Posts
Default

Quote:
Originally Posted by Peter Nelson
Am I right in thinking this can be generalised to larger sizes also?
Sort of. Of course more cache is better if all other things are equal (same CPU stepping and L2 cache latency).

However, 512K is near-ideal for all exponents we are currently testing. So going to 1M and 2M doesn't buy much extra speed. 256K is OK for current double-checks. 128K is real bad.

You might try looking at http://mersenne.org/bench.htm to see the effect of L2 cache on timings. At some FFT size in the distant future a 1M cache will be very important for getting good timings.

Last fiddled with by Prime95 on 2005-10-27 at 00:31
Prime95 is offline   Reply With Quote
Old 2005-10-26, 23:55   #6
Longshot
 
Mar 2004
Somewhere downrange

1410 Posts
Default

Thanks guys. It is nice to be able to tap in to all the expertise here.
Longshot is offline   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
recognizing only 4MB of 8MB L2 cache Dabigley13 Information & Answers 4 2015-05-08 07:45
8k fft and L2 cache pman Information & Answers 1 2012-05-23 14:00
Prime95 and L2 Cache RMAC9.5 Hardware 8 2008-10-29 19:07
Cache Sizes Unregistered Hardware 4 2003-12-06 13:43
L3 cache. What could it buy us? nomadicus Hardware 3 2003-08-09 22:23

All times are UTC. The time now is 19:15.

Thu Aug 6 19:15:32 UTC 2020 up 20 days, 15:02, 2 users, load averages: 2.21, 2.13, 1.92

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.