linux-kernel - Re: [PATCH 5/8] rcu: eliminate deadlock for rcu read site

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Date:	Thu, 22 Aug 2013 10:34:31 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Lai Jiangshan <eag0628@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 5/8] rcu: eliminate deadlock for rcu read site

On Thu, 22 Aug 2013 22:23:09 +0800
Lai Jiangshan <eag0628@...il.com> wrote:


> > By making it a irq-safe lock, we need to disable interrupts every time
> > it is taken, which means the entire pi-chain walk in
> > rt_mutex_adjust_prio_chain() will pretty much be with interrupts
> > disabled.
> 
> 
> I didn't catch your meaning.
> rt_mutex_adjust_prio_chain() is called without wait_lock held.
> current C.S. of wait_lock are really short.
> 

There is quite a bit of overhead to enable and disable interrupts. If
we are doing this in a very fast path, it's going to slow down -rt even
more.

It would be really nice to avoid making wait_lock be irq safe.

-- Steve
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