Messages in this thread | | | Date | Thu, 5 Apr 2012 16:15:33 +0200 (CEST) | From | Pascal CHAPPERON <> | Subject | Re: RCU related performance regression in 3.3 |
| |
Hello,
I didn't notice any significant slowdown while the system is up and running. A full kernel compilation (make -j 16) takes 14mn with both 3.2.10 and 3.3.0.
Pascal
> Message du 05/04/12 16:01 > De : "Paul E. McKenney" > A : "Josh Boyer" > Copie à : linux-kernel@vger.kernel.org, kernel-team@fedoraproject.org, pascal.chapperon@wanadoo.fr > Objet : Re: RCU related performance regression in 3.3 > > On Thu, Apr 05, 2012 at 08:37:59AM -0400, Josh Boyer wrote: > > On Wed, Apr 04, 2012 at 02:36:33PM -0700, Paul E. McKenney wrote: > > > On Wed, Apr 04, 2012 at 11:27:27AM -0400, Josh Boyer wrote: > > > > Hi Paul, > > > > > > > > We've had a few reports of some boot slowdowns with the 3.3 rebase we > > > > did in Fedora 16. One of our users volunteered to bisect a vanilla > > > > kernel and wound up at "rcu: Permit dyntick-idle with callbacks pending > > > > (commit 7cb924990)". You can find more details in the bug [1], but it's > > > > been reported on both physical hardware and in virtual machines. > > > > > > > > Have you seen anything like this in your testing? Given the user used a > > > > vanilla 3.3 kernel, I'm wondering if there is a targetted fix that might > > > > be backported. If so, it would be good to get that headed to the 3.3.y > > > > stable tree. > > > > > > > > josh > > > > > > > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=806548 > > > > > > I will look into this. In the meantime, does setting > > > CONFIG_RCU_FAST_NO_HZ=n get rid of the slowdowns? > > > > Seems so. Pascal tried 3.4-rc1 with and without that set and found that > > disabling it lead to consistent timings. He put his findings in the > > bug, and I've also now CC'd him. > > Thank you for the info! Is the performance problem limited to boot time, > or are there performance problems when the system is up and running? > > Thanx, Paul > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |