linux-kernel - Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree

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Message-ID: <20190809202920.GE255533@google.com>
Date:   Fri, 9 Aug 2019 16:29:20 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     Byungchul Park <byungchul.park@....com>,
        linux-kernel@...r.kernel.org, Rao Shoaib <rao.shoaib@...cle.com>,
        max.byungchul.park@...il.com, kernel-team@...roid.com,
        kernel-team@....com, Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rcu@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu
 batching

On Fri, Aug 09, 2019 at 04:22:26PM -0400, Joel Fernandes wrote:
> > > > o	With any of the above, invoke rcu_momentary_dyntick_idle() along
> > > > 	with cond_resched() in your kfree_rcu() loop.  This simulates
> > > > 	a trip to userspace for nohz_full CPUs, so if this helps for
> > > > 	non-nohz_full CPUs, adjustments to the kernel might be called for.
> 
> I did not try this yet. But I am thinking why would this help in nohz_idle
> case? In nohz_idle we already have the tick active when CPU is idle. I guess
> it is because there may be a long time that elapses before
> rcu_data.rcu_need_heavy_qs == true ?

Sorry, here I meant 'tick active when CPU is not idle'.

thanks,

 - Joel