linux-kernel - Re: [PATCH 3/3] serial: 8250: Add a wakeup

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Message-ID: <20120118041720.GA2431@linux.vnet.ibm.com>
Date:	Tue, 17 Jan 2012 20:17:21 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Simon Glass <sjg@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH 3/3] serial: 8250: Add a wakeup_capable module param

On Tue, Jan 17, 2012 at 08:10:36PM +0000, Alan Cox wrote:
> On Tue, 17 Jan 2012 10:56:03 -0800
> Simon Glass <sjg@...omium.org> wrote:
> 
> > Since serial_core now does not make serial ports wake-up capable by
> > default, add a parameter to support this feature in the 8250 UART.
> > This is the only UART where I think this feature is useful.
> 
> NAK
> 
> Things should just work for users. Magic parameters is not an
> improvement. If its a performance problem someone needs to fix the rcu
> sync overhead or stop using rcu on that path.

I must say that I lack context here, even after looking at the patch,
but the synchronize_rcu_expedited() primitives can be used if the latency
of synchronize_rcu() is too large.

							Thanx, Paul

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