On Wed, Nov 5, 2014 at 3:27 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Wed, 5 Nov 2014 14:50:41 +0100 > Juerg Haefliger <juergh@xxxxxxxxx> wrote: > >> On Sun, Nov 2, 2014 at 8:30 AM, Mike Galbraith <umgwanakikbuti@xxxxxxxxx> >> wrote: >> > >> > On Fri, 2014-10-31 at 17:03 -0400, Steven Rostedt wrote: >> > > Dear RT Folks, >> > > >> > > I'm pleased to announce the 3.14.23-rt20 stable release. >> > > >> > > This is the first 3.14-rt release in the stable-rt series. Normally I >> > > wait till the next development release is out before I pull in a new >> > > one. That is, I would pull in 3.14-rt when 3.16-rt or later was >> > > released. But because development is now moving at a "hobbyist rate" >> > > (read http://lwn.net/Articles/617140/ for details) >> > > and 3.14-rt is no longer being developed against, I figured it was >> > time >> > > to put it under the "stable-rt" umbrella. >> > >> > I piddled about with it yesterday, found that you can't change cpufreq >> > governor IFF the tree is configured as rt, but works fine as voluntary >> > preempt. >> >> The problem seems to be this patch: https://lkml.org/lkml/2014/4/8/584 >> >> The cpufreq code does nested down_read_trylocks and only the first one >> succeeds: >> >> drivers/cpufreq/cpufreq.c: >> store >> down_read_trylock(cpufreq_rwsem) <- succeeds >> store_scaling_governor >> cpufreq_get_policy >> cpufreq_cpu_get >> down_read_trylock(cpufreq_rwsem) <-- fails >> >> Reverting the above patch 'fixes' the problem. I don't understand Steven's >> commit comment that readers of rwsem are not allowed to nest in mainline >> since this works just fine in mainline. > > When we allow multiple readers, this will be allowed. But even in > mainline, if a writer were to come in and block between those two > down_read_trylocks(), the second trylock would fail. Thanks for the explanation. So is this considered a temporary failure until multiple readers are allowed or does cpufreq need fixing or something else? Just trying to figure out what to do next. ...Juerg > PREEMPT_RT just has that fail all the time as we only allow an rwsem to > be held by a single reader. > > > -- Steve > > > >> >> ...Juerg >> >> >> >> > I'll poke about for the entertainment value. Having no >> > personal need/use for rt detracts from its hobby value somewhat, but rt >> > problems do have a tendency to be 'entertaining'. >> > >> > I'll follow up with a few patches that folks can apply to their trees if >> > they so desire. There being no devel tree to submit against, I can't do >> > a proper submission (rules), and some of them you surely don't want :) >> > >> > -Mike >> > >> > >> > >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
