On 26/05/16 12:42, Dmitry Osipenko wrote: > On 26.05.2016 11:42, Jon Hunter wrote: >> >> On 25/05/16 19:51, Dmitry Osipenko wrote: >>> On 25.05.2016 18:09, Jon Hunter wrote: >> >> ... >> >>>> If you are able to reproduce this on v3.18, then it would be good if >>>> you >>>> could trace the CCF calls around this WARNING to see what is causing >>>> the >>>> contention. >>> >>> I managed to reproduce it with some CCF "tracing". >>> Full kmsg log is here: https://bpaste.net/show/d8ab7b7534b7 >>> >>> Looks like CPU freq governor thread yields during clk_set_rate() and >>> then CPU idle kicks in, taking the same mutex. >> >> On the surface that sounds odd to me, but without understanding the >> details, I guess I don't know if this is a valid thing to be doing or >> even how that actually works! >> > > The reason of that happening should be that I'm using clk PRE/POST rate > change notifiers in my DVFS driver that takes other mutexes and they > could be locked, causing schedule. I haven't mentioned it before, sorry. OK, but I am not sure how these "other mutexes" would be relevant here without any more details. > From drivers/clk/clk.c: > > static struct task_struct *prepare_owner; > > ... > > /*** locking ***/ > static void clk_prepare_lock(void) > { > if (!mutex_trylock(&prepare_lock)) { > if (prepare_owner == current) { > prepare_refcnt++; > return; > } > mutex_lock(&prepare_lock); > } > > You can see that it would lock the mutex if prepare_owner != current, in > my case it's idle thread != interactive gov. thread. Right, but that would imply that someone else is actively doing something with a clock. However, if we are entering LP2, then that implies that all CPUs are idle and so I still don't understand the scenario where this would be locked in that case. May be there is something I am overlooking here? >>> However, cpufreq_interactive governor is android specific governor and >>> isn't in upstream kernel yet. Quick googling shows that recent >>> "upstreaming" patch uses same cpufreq_interactive_speedchange_task: >>> https://lkml.org/lkml/2016/5/20/41 >> >> Do you know if this version they are upstreaming could also yield during >> the clk_set_rate()? >> > > I think it should be assumed that any clk_set_rate() potentially could. > Please correct me if I'm wrong. > >>> I'm not aware of other possibility to reproduce this issue, it needs >>> some CCF interaction from a separate task. So the current upstream >>> kernel shouldn't be affected, I guess. >> >> What still does not make sense to me is why any frequency changes have >> not completed before we attempt to enter the LP2 state? >> > Why not? I don't see any CPUIDLE <-> CPUFREQ interlocking. Do you think > it could be harmful somehow? Like I said before, I still don't understand that scenario that is causing this and without being able to fully understand it, I have no idea what the exact problem we are trying to fix here is. Cheers Jon -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
