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From: Joel Fernandes <joel@joelfernandes.org>
To: "Zhang, Qiang" <Qiang.Zhang@windriver.com>
Cc: "paulmck@kernel.org" <paulmck@kernel.org>,
	Uladzislau Rezki <urezki@gmail.com>,
	"josh@joshtriplett.org" <josh@joshtriplett.org>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"mathieu.desnoyers@efficios.com" <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	"rcu@vger.kernel.org" <rcu@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: RCU: Question on force_qs_rnp
Date: Mon, 14 Sep 2020 15:42:08 -0400	[thread overview]
Message-ID: <20200914194208.GA2579423@google.com> (raw)
In-Reply-To: <BYAPR11MB2632C4C06386B39BB5488428FF230@BYAPR11MB2632.namprd11.prod.outlook.com>

On Mon, Sep 14, 2020 at 07:55:18AM +0000, Zhang, Qiang wrote:
> Hello Paul
> 
> I have some questions for you .
> in force_qs_rnp func ,  if  "f(rdp)" func return true we will call rcu_report_qs_rnp func
> report a quiescent state for this rnp node, and clear grpmask form rnp->qsmask.
> after that ,  can we make a check for this rnp->qsmask,  if  rnp->qsmask == 0, 
> we will check blocked readers in this rnp node,  instead of jumping directly to the next node .

Could you clarify what good is this going to do? What problem are you trying to
address?

You could have a task that is blocked in an RCU leaf node, but the
force_qs_rnp() decided to call rcu_report_qs_rnp(). This is perfectly Ok. The
CPU could be dyntick-idle and a quiescent state is reported. However, the GP
must not end and the rcu leaf node should still be present in its parent
intermediate nodes ->qsmask. In this case, the ->qsmask == 0 does not have
any relevance.

Or am I missing the point of the question?

thanks,

 - Joel


  reply	other threads:[~2020-09-14 19:42 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-14  7:55 RCU: Question on force_qs_rnp Zhang, Qiang
2020-09-14 19:42 ` Joel Fernandes [this message]
2020-09-14 20:56   ` Paul E. McKenney
2020-09-15  3:18     ` 回复: " Zhang, Qiang
2020-09-15  3:41       ` Paul E. McKenney
2020-09-15  5:16         ` Zhang,Qiang
2020-09-15 18:06           ` Paul E. McKenney
2020-09-16  6:32             ` Zhang,Qiang

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