Quick FAQ on Forceasm, Advmethods, and Overclocking

mmonnin

http://forum.folding-community.org/posting.php?mode=quote&p=47189

I would appreciate it if anyone using these three techniques would please read this post. As you may or may not have realized, a number of members here have been complaining about work unit stability, specifically P3xx and P10xx series units. This small "mini-FAQ" intends to explain the effect of the three techniques above on stability, and what to do if you are having problems.

The first thing to remember is that "-forceasm" and overclocking both involve a tradeoff: you are trading the stability of the client for speed. The client's default settings and your machine's stock settings are both optimized for stability. When you apply "-forceasm" or OC your machine, you are giving up the stable defaults in favor of completing units "faster." The problem is that "faster" isn't always faster. Sometimes, the errors generated as a result of these methods will result in an overall speed loss: your machine is so unstable that it is unable to complete a significant fraction of its assigned work units. This is a bad thing for all involved. "-forceasm" forces on SIMD instructions that the client may have otherwise determined were unusuable due to stability problems. These instruction sets are usually faster, but if they don't work right, why use them?

"-advmethods" is different than either "-forceasm" or overclocking. "-advmethods" is a special client flag that signifies that you are willing to accept beta work units to be tested. Most of these work units have been stable, but lately people have been receiving units, using "-advmethods", that have not been processed properly. Most likely, this is the result of either of the two options described above. However, when using "-advmethods", you agree to accept beta test work units that may or may not be considered stable. In the past, units assigned under "-advmethods" have been the desirable Gromacs units, and this was the only way to get them. This is no longer true. Gromacs units are now distributed widely to clients not using any flags at all. In fact, I would expect to soon see a drop in the number of Gromacs core units on "-advmethods", as a new F@H core is released that will require beta testing. When, or if, this will happen is not known.

The end result of any of these three options is that you may be seeing stability problems where there have not been any in the past. P3xx and P10xx series work units seem to push machines much harder than other work units we have before. If you are seeing problems, the typical troubleshooting procedure we will ask you to follow where one or more of these options is used will look like this:

1. Reduce or remove any overclock that may be present. Overclocking your system beyond its rated specs always brings the possibility of large stability problems. Gromacs, in particular, has been known to highlight these problems. So, the first thing to do is reduce your OC.
2. Remove "-forceasm". If you remove this flag, you will be running with what the client considers the best SIMD instructions for your machine. You may incur a speed penalty, but which would you rather have: a working client, or a faster client that has errors on, in some cases, all of its work units, causing them never to be credited?
3. Remove "-advmethods". Using "-advmethods", as mentioned, means you agree to accept work units that are in the late beta stages of testing. They cannot be guaranteed stable; by definition, they are still under testing. If you cannot process "-advmethods" units, please do everyone involved a favor and remove the flag.

If you are still experiencing issues after going through the above list, please post a topic here. We will do our best to help you sort out any problems.

Quick and dirty.

Got any more Qs please ask.

Spinner

Somebody sticky this. This is the sort of info I'm always trying to find in this forum but never can without a 30minute search.

EDIT: A wise choice young master. Very good.;)