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Date: Wed, 24 Jun 2015 15:43:37 +0200 From: Ingo Molnar <mingo@...nel.org> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@...radead.org>, Oleg Nesterov <oleg@...hat.com>, tj@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net, riel@...hat.com, viro@...IV.linux.org.uk, torvalds@...ux-foundation.org Subject: Re: [RFC][PATCH 12/13] stop_machine: Remove lglock * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote: > On Wed, Jun 24, 2015 at 10:42:48AM +0200, Ingo Molnar wrote: > > > > * Peter Zijlstra <peterz@...radead.org> wrote: > > > > > On Tue, Jun 23, 2015 at 11:26:26AM -0700, Paul E. McKenney wrote: > > > > > > > > > > I really think you're making that expedited nonsense far too accessible. > > > > > > > > This has nothing to do with accessibility and everything to do with > > > > robustness. And with me not becoming the triage center for too many non-RCU > > > > bugs. > > > > > > But by making it so you're rewarding abuse instead of flagging it :-( > > > > Btw., being a 'triage center' is the bane of APIs that are overly successful, > > so we should take that burden with pride! :-) > > I will gladly accept that compliment. > > And the burden. But, lazy as I am, I intend to automate it. ;-) lol :) > > Lockdep (and the scheduler APIs as well) frequently got into such situations as > > well, and we mostly solved it by being more informative with debug splats. > > > > I don't think a kernel API should (ever!) stay artificially silent, just for fear > > of flagging too many problems in other code. > > I agree, as attested by RCU CPU stall warnings, lockdep-RCU, sparse-based > RCU checks, and the object-debug-based checks for double call_rcu(). > That said, in all of these cases, including your example of lockdep, > the diagnostic is a debug splat rather than a mutex-contention meltdown. > And it is the mutex-contention meltdown that I will continue making > synchronize_sched_expedited() avoid. > > But given the change from bulk try_stop_cpus() to either stop_one_cpu() or > IPIs, it would not be hard to splat if a given CPU didn't come back fast > enough. The latency tracer would of course provide better information, > but synchronize_sched_expedited() could do a coarse-grained job with > less setup required. > > My first guess for the timeout would be something like 500 milliseconds. > Thoughts? So I'd start with 5,000 milliseconds and observe the results first ... Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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