On Sat, Mar 21, 2009 at 10:53:18PM -0700, Arjan van de Ven wrote: > On Sat, 21 Mar 2009 22:18:22 -0700 > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > I'm measuring the time that the following code takes: > > > > > > init_completion(&rcu.completion); > > > /* Will wake me after RCU finished. */ > > > call_rcu(&rcu.head, wakeme_after_rcu); > > > /* Wait for it. */ > > > wait_for_completion(&rcu.completion); > > > > > > > > No, my confusion -- I misread as 2700 milliseconds rather than 2700 > > -microseconds-. 2700 microseconds (or 2.7 milliseconds) is in the > > expected range for synchronize_rcu() on an HZ=1000 system. 2.7 > > seconds would of course be way out of line. > > > > > If the former, exactly which kernel are you using? The single-CPU > > > > optimization was added in 2.6.29-rc7, commit ID a682604838. > > > > > > a bit after -rc8, specifically commit > > > 5bee17f18b595937e6beafeee5197868a3f74a06 > > > > How many synchronize_rcu() calls are you seeing on the boot path? > > I see 20 that hit the above code path (eg ones that wait) until > userspace starts. So with well-behaved readers, the full sequence would be worth something like 50-60 milliseconds. > > Also, are you running with NO_HZ=y? > > of course... is there any other way ? ;-) Well, if it does become necessary to make common-case no-readers execution of synchronize_rcu() go faster, you certainly have made the correct choice. ;-) 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
