From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932872Ab2ASTvu (ORCPT ); Thu, 19 Jan 2012 14:51:50 -0500 Received: from mail-tul01m020-f174.google.com ([209.85.214.174]:52771 "EHLO mail-tul01m020-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932670Ab2ASTvs convert rfc822-to-8bit (ORCPT ); Thu, 19 Jan 2012 14:51:48 -0500 MIME-Version: 1.0 In-Reply-To: <20120119194242.GE2373@linux.vnet.ibm.com> References: <1327001336-28703-1-git-send-email-sjg@chromium.org> <20120119194242.GE2373@linux.vnet.ibm.com> Date: Thu, 19 Jan 2012 11:51:47 -0800 X-Google-Sender-Auth: 55mmxl8uvCAVC1AqaWCl6uA4wEU Message-ID: Subject: Re: [PATCH] serial: Fix wakeup init logic to speed up startup From: Simon Glass To: paulmck@linux.vnet.ibm.com Cc: LKML , Greg Kroah-Hartman , linux-serial@vger.kernel.org, "Rafael J. Wysocki" , Alan Cox X-System-Of-Record: true Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, On Thu, Jan 19, 2012 at 11:42 AM, Paul E. McKenney wrote: > 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. Yes that's right, although I didn't get different behavior with 'nosmp'. > > The patch looks good to me, but then again, I do not consider myself > qualified to have an opinion on the TTY layer.  ;-) Thanks, me neither :-) Regards, Simon > >                                                        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 >> >