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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Ankur Arora <ankur.a.arora@oracle.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de,
	paulmck@kernel.org, mingo@kernel.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	vschneid@redhat.com, frederic@kernel.org, efault@gmx.de
Subject: Re: [PATCH 6/7] osnoise: handle quiescent states for PREEMPT_RCU=n,
 PREEMPTION=y
Message-ID: <20241010065338.sw4zZlbm@linutronix.de>
References: <20241009165411.3426937-1-ankur.a.arora@oracle.com>
 <20241009165411.3426937-7-ankur.a.arora@oracle.com>
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In-Reply-To: <20241009165411.3426937-7-ankur.a.arora@oracle.com>

On 2024-10-09 09:54:10 [-0700], Ankur Arora wrote:
> To reduce RCU noise for nohz_full configurations, osnoise depends
> on cond_resched() providing quiescent states for PREEMPT_RCU=n
> configurations. And, for PREEMPT_RCU=y configurations does this
> by directly calling rcu_momentary_eqs().
> 
> With PREEMPT_LAZY=y, however, we can have configurations with
> (PREEMPTION=y, PREEMPT_RCU=n), which means neither of the above
> can help.

PREEMPTION=y, PREEMPT_RCU=n should not be possible.

> Handle that by fallback to the explicit quiescent states via
> rcu_momentary_eqs().

Sebastian