Andy Pugh wrote: > 2010/1/27 Gene Heskett<[email protected]>: > >>> and the dual core can keep RT and video threads separate. >>> >> Only if you can convince linux to keep them separated, and I'm not aware of >> anyone doing that successfully. >> > I _think_ I might be (with a dual-CPU system). Running an SMP system > and ISOLCPUS=1 in the grub options is alleged to keep the RT threads > running on a CPU all to themselves. > S W Padnos has hinted it isn't that simple on the IRC chat, but I > think for practical purposes it works. I have a latency off 6000 now, > whereas it used to be 18000 > It is that simple to tell Linux to leave a core out of normal scheduling. It just doesn't always work out as well as one would like.
I have a Core2 Duo system (four of them actually) that are using an older SMP kernel and isolcpus. The latency on those systems is phenomenal, but only if I "load" the non-RT core with a do-nothing application. It quite literally does nothing: while true ; do echo "nothing" > /dev/null ; done That lowers the latencies on the RT side to under 2000, and usually in the 200-800 range (down from 8000-10000). That system has been heavily optimized for headless embedded operation though, and even using the network a lot can cause latency spikes to the 10000 range. There was a spike every 5 seconds, which I narrowed down to kjournald (the thing that makes ext3 safer than ext2). The disk is a small SSD, formatted as ext2 and mounted read-only. The system does not boot to a graphical login, and networking is normally unused. The bottom line is that isolcpus and RT-SMP are just a couple of tools in a big kit, and won't always show the excellent results you're seeing. (I wish they would :) ) - Steve ps: note that the do-nothing trick only seems to work on Intel CPUs. I think we tried it on an AMD and saw no change (as should be expected). ------------------------------------------------------------------------------ The Planet: dedicated and managed hosting, cloud storage, colocation Stay online with enterprise data centers and the best network in the business Choose flexible plans and management services without long-term contracts Personal 24x7 support from experience hosting pros just a phone call away. http://p.sf.net/sfu/theplanet-com _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
