From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932832Ab2ASTnY (ORCPT ); Thu, 19 Jan 2012 14:43:24 -0500 Received: from e38.co.us.ibm.com ([32.97.110.159]:59119 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932807Ab2ASTnW (ORCPT ); Thu, 19 Jan 2012 14:43:22 -0500 Date: Thu, 19 Jan 2012 11:42:42 -0800 From: "Paul E. McKenney" To: Simon Glass Cc: LKML , Greg Kroah-Hartman , linux-serial@vger.kernel.org, "Rafael J. Wysocki" , Alan Cox Subject: Re: [PATCH] serial: Fix wakeup init logic to speed up startup Message-ID: <20120119194242.GE2373@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1327001336-28703-1-git-send-email-sjg@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1327001336-28703-1-git-send-email-sjg@chromium.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12011919-5518-0000-0000-000001A91D63 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 19, 2012 at 11:28:56AM -0800, Simon Glass wrote: > The synchronize_rcu() call resulting from making every serial driver > wake-up capable (commit b3b708fa) slows boot down on my Tegra2x system > (with CONFIG_PREEMPT disabled). > > But this is avoidable since it is the device_set_wakeup_enable() and then > subsequence disable which causes the delay. We might as well just make > the device wakeup capable but not actually enable it for wakeup until > needed. > > Effectively the current code does this: > > device_set_wakeup_capable(dev, 1); > device_set_wakeup_enable(dev, 1); > device_set_wakeup_enable(dev, 0); > > We can just drop the last two lines. > > Before this change my boot log says: > [ 0.227062] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled > [ 0.702928] serial8250.0: ttyS0 at MMIO 0x70006040 (irq = 69) is a Tegra > > after: > [ 0.227264] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled > [ 0.227983] serial8250.0: ttyS0 at MMIO 0x70006040 (irq = 69) is a Tegra > > for saving of 450ms. You have multiple CPUs running at this point, correct? Before that second CPU starts up, synchronize_rcu() is a no-op. The patch looks good to me, but then again, I do not consider myself qualified to have an opinion on the TTY layer. ;-) Thanx, Paul > Suggested-by: Rafael J. Wysocki > Signed-off-by: Simon Glass > --- > drivers/tty/serial/serial_core.c | 6 +++--- > 1 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index c7bf31a..1305618 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -2348,11 +2348,11 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport) > */ > tty_dev = tty_register_device(drv->tty_driver, uport->line, uport->dev); > if (likely(!IS_ERR(tty_dev))) { > - device_init_wakeup(tty_dev, 1); > - device_set_wakeup_enable(tty_dev, 0); > - } else > + device_set_wakeup_capable(tty_dev, 1); > + } else { > printk(KERN_ERR "Cannot register tty device on line %d\n", > uport->line); > + } > > /* > * Ensure UPF_DEAD is not set. > -- > 1.7.7.3 >