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Message-ID: <20160507152501.GW3593@linux.vnet.ibm.com> Date: Sat, 7 May 2016 08:25:01 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Ross Green <rgkernel@...il.com> Cc: Peter Zijlstra <peterz@...radead.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, "Chatre, Reinette" <reinette.chatre@...el.com>, Jacob Pan <jacob.jun.pan@...ux.intel.com>, Josh Triplett <josh@...htriplett.org>, John Stultz <john.stultz@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, dipankar@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>, rostedt <rostedt@...dmis.org>, David Howells <dhowells@...hat.com>, Eric Dumazet <edumazet@...gle.com>, Darren Hart <dvhart@...ux.intel.com>, Frédéric Weisbecker <fweisbec@...il.com>, Oleg Nesterov <oleg@...hat.com>, pranith kumar <bobby.prani@...il.com> Subject: Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17 On Fri, May 06, 2016 at 04:25:16PM +1000, Ross Green wrote: > On Sun, Apr 3, 2016 at 6:18 PM, Paul E. McKenney > <paulmck@...ux.vnet.ibm.com> wrote: > > On Thu, Mar 31, 2016 at 08:42:55AM -0700, Paul E. McKenney wrote: > >> On Wed, Mar 30, 2016 at 07:55:47AM -0700, Paul E. McKenney wrote: > >> > On Tue, Mar 29, 2016 at 06:49:08AM -0700, Paul E. McKenney wrote: > >> > > On Mon, Mar 28, 2016 at 05:28:14PM -0700, Paul E. McKenney wrote: > >> > > > On Mon, Mar 28, 2016 at 05:25:18PM -0700, Paul E. McKenney wrote: > >> > > > > On Mon, Mar 28, 2016 at 06:08:41AM -0700, Paul E. McKenney wrote: > >> > > > > > On Mon, Mar 28, 2016 at 08:25:47AM +0200, Peter Zijlstra wrote: > >> > > > > > > On Sun, Mar 27, 2016 at 02:06:41PM -0700, Paul E. McKenney wrote: > >> > > > > > >> > > > > [ . . . ] > >> > > > > > >> > > > > > > > OK, so I should instrument migration_call() if I get the repro rate up? > >> > > > > > > > >> > > > > > > Can do, maybe try the below first. (yes I know how long it all takes :/) > >> > > > > > > >> > > > > > OK, will run this today, then run calibration for last night's run this > >> > > > > > evening. > >> > > > >> > > And of 18 two-hour runs, there were five failures, or about 28%. > >> > > That said, I don't have even one significant digit on the failure rate, > >> > > as 5 of 18 is within the 95% confidence limits for a failure probability > >> > > as low as 12.5% and as high as 47%. > >> > > >> > And after last night's run, this is narrowed down to between 23% and 38%, > >> > which is close enough. Average is 30%, 18 failures in 60 runs. > >> > > >> > Next step is to test Peter's patch some more. Might take a couple of > >> > night's worth of runs to get statistical significance. After which > >> > it will be time to rebase to 4.6-rc1. > >> > >> And the first night was not so good: 6 failures out of 24 runs. Adding > >> this to the 1-of-10 earlier gets 7 failures of 34. Here are how things > >> stack up given the range of base failure estimates: > >> > >> Low 95% bound of 23%: 84% confidence. > >> > >> Actual measurement of 30%: 92% confidence. > >> > >> High 95% bound of 38%: 98% confidence. > >> > >> So there is still some chance that Peter's patch is helping. I will > >> run for one more evening, after which it will be time to move forward > >> to 4.6-rc1. > > > > And no luck reducing bounds. However, moving to 4.6-rc1 did get some > > of the trace_printk() to print. The ftrace_dump()s resulted in RCU > > CPU stall warnings, and the dumps were truncated due to test timeouts > > in my scripting. (I need to make my scripts more patient when they > > see an ftrace dump in progress, I guess.) > > > > Here are the results: > > > > http://www2.rdrop.com/users/paulmck/submission/TREE03.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.1.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.2.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.3.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.4.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.5.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.6.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.7.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.8.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.9.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.11.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.12.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.13.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.14.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.15.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.16.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.17.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.18.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.19.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.20.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.21.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.22.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.23.console.log.tgz > > http://www2.rdrop.com/users/paulmck/submission/TREE03.24.console.log.tgz > > > > The config is here: > > > > http://www2.rdrop.com/users/paulmck/submission/config.tgz > > > > More runs to measure 4.6-rc1 base error rate... > > > > Thanx, Paul > > > G'day Paul, > > > Thought i would update a few runs with the linux-4.6-rc kernels. > > I have attached log outputs through dmesg showing rcu_preempt stall warnings. > > > Thought it might be interesting for someone else to look at. > > Currently running linux-4.6-rc6 in testing. Thank you for sending these, I will look them over! Still working to reproduce this quickly enough to do real debug... :-/ Thanx, Paul
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