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From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>,
	hpa@zytor.com, josh@joshtriplett.org, rostedt@goodmis.org,
	mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
	torvalds@linux-foundation.org, mingo@kernel.org,
	tglx@linutronix.de, linux-kernel@vger.kernel.org,
	oleg@redhat.com, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:sched/core] sched/core: Avoid _cond_resched() for PREEMPT=y
Date: Fri, 23 Sep 2016 10:44:42 +0200	[thread overview]
Message-ID: <20160923084442.GC5008@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160922202817.GT14933@linux.vnet.ibm.com>

On Thu, Sep 22, 2016 at 01:28:17PM -0700, Paul E. McKenney wrote:
> On Thu, Sep 22, 2016 at 08:42:28PM +0200, Peter Zijlstra wrote:
> > 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")
> 
> I would instead say that we changed the algorithm to reduce the overhead
> in the common case, but yes, this commit did change things quite a bit.

Sure, but critical point (for this discussion) is that cond_resched() no
longer implies anything RCU, it really only is a voluntary reschedule
point.

  reply	other threads:[~2016-09-23  8:44 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <tip-35a773a07926a22bf19d77ee00024522279c4e68@git.kernel.org>
2016-09-22 18:25 ` [tip:sched/core] sched/core: Avoid _cond_resched() for PREEMPT=y Mikulas Patocka
2016-09-22 18:30   ` Paul E. McKenney
2016-09-22 18:42   ` Peter Zijlstra
2016-09-22 20:28     ` Paul E. McKenney
2016-09-23  8:44       ` Peter Zijlstra [this message]
2016-09-23 14:47         ` Paul E. McKenney

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