On Sat, Mar 21, 2009 at 09:26:08PM +0100, Eric Dumazet wrote: > Arjan van de Ven a écrit : > > On Fri, 20 Mar 2009 18:27:46 -0700 > > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > >> On Fri, Mar 20, 2009 at 11:13:54AM -0700, Arjan van de Ven wrote: > >>> On Fri, 20 Mar 2009 07:31:04 -0700 > >>> "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > >>>>> that'd be throwing out the baby with the bathwater... I'm > >>>>> trying to use the other cpus to do some of the boot work (so > >>>>> that the total goes faster); not using the other cpus would be > >>>>> counter productive to that. (As is just sitting in > >>>>> synchronize_rcu() when the other cpu is working.. hence this > >>>>> discussion ;-) > >>>> OK, so you are definitely running multiple CPUs when the offending > >>>> synchronize_rcu() executes, then? > >>> absolutely. > >>> (and I'm using bootgraph.pl in scripts to track who's stalling etc) > >>>> If so, here are some follow-on questions: > >>>> > >>>> 1. How many synchronize_rcu() calls are you seeing on the > >>>> critical boot path > >>> I've seen only this (input) one to take a long time > >> Ouch!!! A -single- synchronize_rcu() taking a full second??? That > >> indicates breakage. > >> > >>>> and what value of HZ are you running? > >>> 1000 > >> K, in absence of readers for RCU_CLASSIC, we should see a handful > >> of milliseconds for synchronize_rcu(). > > > > I've attached an instrumented bootgraph of what is going on; > > the rcu delays are shown as red blocks inside the regular functions > > as they initialize...... > > > > (svg can be viewed with inkscape, gimp, firefox and various other tools) > > Interesting stuff... > > I thought you mentioned i2c drivers being source of the udelays(), > but I cant see them in this svg, unless its async_probe_hard ? Arjan, another thought -- if the udelays() are not under rcu_read_lock(), you should be able to finesse this by using CONFIG_PREEMPT_RCU, which will happily ignore spinning CPUs as long as they are not in an RCU read-side critical section. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
