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Date: Thu, 7 Oct 2021 02:18:43 +0200 From: Frederic Weisbecker <frederic@...nel.org> To: Valentin Schneider <valentin.schneider@....com> Cc: "Paul E . McKenney" <paulmck@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, Uladzislau Rezki <urezki@...il.com>, Thomas Gleixner <tglx@...utronix.de>, Boqun Feng <boqun.feng@...il.com>, Neeraj Upadhyay <neeraju@...eaurora.org>, Josh Triplett <josh@...htriplett.org>, Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org Subject: Re: [PATCH 10/11] rcu: Apply callbacks processing time limit only on softirq On Wed, Oct 06, 2021 at 04:12:12PM +0100, Valentin Schneider wrote: > On 04/10/21 15:47, Frederic Weisbecker wrote: > > On Fri, Oct 01, 2021 at 06:51:32PM +0100, Valentin Schneider wrote: > >> On 30/09/21 00:10, Frederic Weisbecker wrote: > >> > Time limit only makes sense when callbacks are serviced in softirq mode > >> > because: > >> > > >> > _ In case we need to get back to the scheduler, > >> > cond_resched_tasks_rcu_qs() is called after each callback. > >> > > >> > _ In case some other softirq vector needs the CPU, the call to > >> > local_bh_enable() before cond_resched_tasks_rcu_qs() takes care about > >> > them via a call to do_softirq(). > >> > > >> > _ The time spent on other tasks after scheduling out, or on softirqs > >> > processing, is spuriously accounted to the time limit. > >> > > >> > >> That wasn't the case before ("rcu: Fix callbacks processing time limit > >> retaining cond_resched()") > > > > But if cond_resched_tasks_rcu_qs() was called and then on the next iteration > > tlimit is checked, the time spent scheduling out is included, right? > > > > if tlimit was set, then that branch would either continue or break; both > cases would have skipped over the cond_resched_tasks_rcu_qs() (which the > aforementioned patch addresses). Duh, right indeed. I need to clarify the changelog. Thanks!
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