> From: Paul E. McKenney Sent: 08/24/13 02:18 AM > On Fri, Aug 23, 2013 at 03:20:25PM +0200, Tibor Billes wrote: > > > From: Paul E. McKenney Sent: 08/22/13 12:09 AM > > > On Wed, Aug 21, 2013 at 11:05:51PM +0200, Tibor Billes wrote: > > > > > From: Paul E. McKenney Sent: 08/21/13 09:12 PM > > > > > 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. > > > > > > > > I don't specifically need this config option so I'm fine without it in > > > > the long term, but I guess it's not supposed to behave like that. > > > > > > OK, good, we have a long-term workload for your specific case, > > > even better. ;-) > > > > > > But yes, there are situations where RCU_FAST_NO_HZ needs to work > > > a bit better. I hope you will bear with me with a bit more > > > testing... > > > > Don't worry, I will :) Unfortunately I didn't have time yesterday and I > > won't have time today either. But I'll do what you asked tomorrow and I'll > > send you the results. > > Not a problem! I did find one issue that -might- help, please see > the patch below. (Run with CONFIG_RCU_FAST_NO_HZ=y.) > > Please let me know how it goes!
I applied the patch on top of 3.11-rc6, but it did not help, I'm still hitting this issue. Let me know if you have anything else that I can test! Tibor -- 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/
