From mboxrd@z Thu Jan 1 00:00:00 1970 From: paulmck@linux.vnet.ibm.com (Paul E. McKenney) Date: Fri, 3 Feb 2012 11:26:55 -0800 Subject: [PATCH RFC idle 2/3] arm: Avoid invoking RCU when CPU is idle In-Reply-To: <87ty37689a.fsf@ti.com> References: <1328143404-11038-2-git-send-email-paulmck@linux.vnet.ibm.com> <20120202044439.GD2435@linux.vnet.ibm.com> <20120202174337.GS2518@linux.vnet.ibm.com> <20120202190708.GE2518@linux.vnet.ibm.com> <87obtgc1xx.fsf@ti.com> <20120202230326.GJ2518@linux.vnet.ibm.com> <87ty37689a.fsf@ti.com> Message-ID: <20120203192655.GJ2382@linux.vnet.ibm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Feb 03, 2012 at 11:12:49AM -0800, Kevin Hilman wrote: > "Paul E. McKenney" writes: > > > On Thu, Feb 02, 2012 at 02:20:26PM -0800, Kevin Hilman wrote: > >> "Paul E. McKenney" writes: > >> > >> [...] > >> > >> >> > The two options I see are: > >> >> > > >> >> > 1. Rip tracing out of the inner idle loops and everything that > >> >> > they invoke. > >> >> > >> >> What I suggested above. But as I said I know sh*t about that tracing > >> >> implementation so that's an easy suggestion for me to make. > >> > > >> > Works for me as well. ;-) > >> > >> While I must admit not having a better suggestion, I for one would vote > >> strongly against removing tracing from the idle path. > >> > >> Being a PM developer and maintainer, much of the code I work on and > >> maintain happens to be run in the bowels of the idle path. Not having > >> the ability to trace this code would be a major step backwards IMO. > > > > OK... > > > > What if the tracing code between the rcu_idle_enter() and the > > rcu_idle_exit() had to be enclosed in a wrapper? For example, > > the tracing in cpuidle_idle_call() might appear as follows: > > > > RCU_NONIDLE( > > trace_power_start(POWER_CSTATE, next_state, dev->cpu); > > trace_cpu_idle(next_state, dev->cpu); > > ); > > > > entered_state = target_state->enter(dev, drv, next_state); > > > > RCU_NONIDLE( > > trace_power_end(dev->cpu); > > trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu); > > ); > > > > The RCU_NONIDLE() macro would do rcu_idle_exit(), execute its > > argument, then do rcu_idle_enter(). (Credit to Steven Rostedt > > for suggesting this.) Given the possibility of code invoked both > > from idle and not-idle, I have some changes to rcu to allow nesting > > of rcu_idle_enter() and rcu_idle_exit(). > > > > Would that work for you? > > Yes, that should work. > > And I defintely have examples of code paths that use tracepoints in both > idle and non-idle context (power domains, clocks, etc.) so the changes > to allow nesting will be needed. OK, good to know that my paranoia is still functioning correctly. ;-) Thanx, Paul