Oh crap. I just realized this is an older version of the patch..mustv'e forgot to refresh...grr. Ill send out the refreshed one. But anyway, I digress. On Thu, 2007-10-25 at 11:27 -0400, Steven Rostedt wrote: > > The cpu_priority and the cp->lock will be aboslutely horrible for > cacheline bouncing. In the form presented here in this email, perhaps. I think you will see some significant improvements in the refreshed version. The big change is that the global lock is gone. > Ironically, this will kill performance for the very > machines this code is to help with. The larger the number of CPUs you > have the more cacheline bouncing this code will create. Don't forget: The same is precisely true for the current -rt2 algorithm. For instance, the -rt2 algorithm aside from being linear in general, scales cacheline bouncing linearly as well. Each cpu is going to trash rq->rt.highest_prio and then we will walk them for each scan. The fact is, you can't maintain a global dynamic policy without bouncing cachelines, period. But hopefully we can minimize it, and I just want to see the fastest code here. > > I still don't see the benefit from the cpupri code. I still owe you timing data, but at this juncture I think I can beat linear (especially as we start throwing in big-iron) ;) I originally got involved in this scheduler rework from observations of poor scaling on our 8/16-ways, so I want it to scale as much as you ;) If this alg doesn't pan out, that's cool. But I think it will in the end. Linear algs in the fast path just make my skin crawl. Perhaps it will still be the best design in the end, but I am not giving up that easy until I prove it to myself. Regards, -Greg
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