* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 23 Mar 2010 18:34:09 +0100 > Ingo Molnar <mingo@xxxxxxx> wrote: > > > > > It shows a very brutal amount of page fault invoked mmap_sem spinning > > overhead. > > > > Yes. Note that we fall off a cliff at nine threads on a 16-way. As soon as > a core gets two threads scheduled onto it? it's AMD Opterons so no SMT. My (wild) guess would be that 8 cpus can still do cacheline ping-pong reasonably efficiently, but it starts breaking down very seriously with 9 or more cores bouncing the same single cache-line. Breakdowns in scalability are usually very non-linear, for hardware and software reasons. '8 threads' sounds like a hw limit to me. From the scheduler POV there's no big difference between 8 or 9 CPUs used [this is non-HT] - with 8 or 7 cores still idle. Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>