On 10/16/07, Siddha, Suresh B <[EMAIL PROTECTED]> wrote: > On Tue, Oct 16, 2007 at 12:07:06PM -0700, Ken Chen wrote: > > We recently discovered a nasty performance bug in the kernel CPU load > > balancer where we were hit by 50% performance regression. > > > > When tasks are assigned to a subset of CPUs that span across > > sched_domains (either ccNUMA node or the new multi-core domain) via > > cpu affinity, kernel fails to perform proper load balance at > > these domains, due to several logic in find_busiest_group() miss > > identified busiest sched group within a given domain. This leads to > > inadequate load balance and causes 50% performance hit. > > > > To give you a concrete example, on a dual-core, 2 socket numa system, > > there are 4 logical cpu, organized as: > > oops, this issue can easily happen when cores are not sharing caches. I > think this is what happening on your setup, right?
yes, we observed the bad behavior on quad-core system with separate L2 cache as well. - Ken - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
