Messages in this thread | | | Date | Thu, 5 Apr 2012 08:37:59 -0400 | From | Josh Boyer <> | Subject | Re: RCU related performance regression in 3.3 |
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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.
josh
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