On Fri, Apr 08, 2022 at 11:46:15PM +0200, Uladzislau Rezki wrote: > > > > Here is what I believe you are proposing: > > > > > > --- rcu_nocbs rcu_nocbs=??? > > > > CONFIG_RCU_NOCB_CPU_ALL=n [1] [2] [3] > > > > CONFIG_RCU_NOCB_CPU_ALL=y [4] [4] [3] > > > > > > [1] No CPUs are offloaded at boot. CPUs cannot be offloaded at > > runtime. > > > > [2] No CPUs are offloaded at boot, but any CPU can be offloaded > > (and later de-offloaded) at runtime. > > > > [3] The set of CPUs that are offloaded at boot are specified by the > > mask, represented above with "???". The CPUs that are offloaded > > at boot can be de-offloaded and offloaded at runtime. The CPUs > > not offloaded at boot cannot be offloaded at runtime. > > > > [4] All CPUs are offloaded at boot, and any CPU can be de-offloaded > > and offloaded at runtime. This is the same behavior that > > you would currently get with CONFIG_RCU_NOCB_CPU_ALL=n and > > rcu_nocbs=0-N. > > > > > > I am adding Frederic on CC, who will not be shy about correcting any > > confusion I be suffering from have with respect to the current code. > > > > Either way, if this is not what you had in mind, what are you suggesting > > instead? > > > > I believe that Steve Rostedt's review would carry weight for ChromeOS, > > however, I am suffering a senior moment on the right person for Android. > > > We(in Sony) mark all CPUs as offloaded ones because of power reasons. The > energy aware scheduler has a better knowledge where to place an rcuop/x > task to invoke callbacks. The decision is taken based on many reason and > the most important is to drain less power as a result of task placement. > For example, power table, if OPP becomes higher or not, CPU is idle, etc. > > What Joel does in this patch sounds natural to me at least from the first > glance. I mean converting the RCU_NOCB_CPU=y to make all CPUs to do offloading. Just to be very clear, given appropriate acks/reviews, adding something like CONFIG_RCU_NOCB_CPU_ALL to get default rcu_nocbs=0-N is fine. However, Joel's original patch would not be good for the enterprise distros, which rely on the current default. Thanx, Paul
