On Wed, Aug 21, 2013 at 08:14:46PM +0200, Tibor Billes wrote: > > From: Paul E. McKenney Sent: 08/20/13 11:43 PM > > On Tue, Aug 20, 2013 at 10:52:26PM +0200, Tibor Billes wrote: > > > > From: Paul E. McKenney Sent: 08/20/13 04:53 PM > > > > On Tue, Aug 20, 2013 at 08:01:28AM +0200, Tibor Billes wrote: > > > > > Hi, > > > > > > > > > > I was using the 3.9.7 stable release and tried to upgrade to the > > > > > 3.10.x series. > > > > > The 3.10.x series was showing unusually high (>75%) system CPU usage > > > > > in some > > > > > situations, making things really slow. The latest stable I tried is > > > > > 3.10.7. > > > > > I also tried 3.11-rc5, they both show this behaviour. This behaviour > > > > > doesn't > > > > > show up when the system is idling, only when doing some CPU intensive > > > > > work, > > > > > like compiling with multiple threads. Compiling with only one thread > > > > > seems not > > > > > to trigger this behaviour. > > > > > > > > > > To be more precise I did a `perf record -a` while compiling a large > > > > > C++ program > > > > > with scons using 4 threads, the result is appended at the end of this > > > > > email. > > > > > > > > New one on me! You are running a mainstream system (x86_64), so I am > > > > surprised no one else noticed. > > > > > > > > Could you please send along your .config file? > > > > > > Here it is > > > > Interesting. I don't see RCU stuff all that high on the list, but > > the items I do see lead me to suspect RCU_FAST_NO_HZ, which has some > > relevance to the otherwise inexplicable group of commits you located > > with your bisection. Could you please rerun with CONFIG_RCU_FAST_NO_HZ=n? > > > > If that helps, there are some things I could try. > > It did help. I didn't notice anything unusual when running with > CONFIG_RCU_FAST_NO_HZ=n.
Interesting. Thank you for trying this -- and we at least have a short-term workaround for this problem. I will put a patch together for further investigation. In the meantime, could you please tell me how you were measuring performance for your kernel builds? Wall-clock time required to complete one build? Number of builds completed per unit time? Something else? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/