linux-kernel - Re: [tip:sched/core] sched/core: Avoid _cond

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Message-ID: <20160922184228.GA5012@twins.programming.kicks-ass.net>
Date:   Thu, 22 Sep 2016 20:42:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     hpa@...or.com, paulmck@...ux.vnet.ibm.com, josh@...htriplett.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, torvalds@...ux-foundation.org,
        mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        oleg@...hat.com, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched/core: Avoid _cond_resched() for PREEMPT=y

On Thu, Sep 22, 2016 at 02:25:01PM -0400, Mikulas Patocka wrote:
> I've found a document that says that cond_resched() is needed on
> preemptible kernels to mark RCU quiescent states:
> 
> https://lwn.net/Articles/603252/
> 
> Paul, is cond_resched() still needed on current RCU implementation? Or not?

No, we ripped that out. See 4a81e8328d37 ("rcu: Reduce overhead of
cond_resched() checks for RCU")