Messages in this thread | | | Date | Thu, 19 Jan 2012 11:51:47 -0800 | Subject | Re: [PATCH] serial: Fix wakeup init logic to speed up startup | From | Simon Glass <> |
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Hi Paul,
On Thu, Jan 19, 2012 at 11:42 AM, Paul E. McKenney <paulmck@linux.vnet.ibm.com> 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 <rjw@sisk.pl> >> Signed-off-by: Simon Glass <sjg@chromium.org> >> --- >> 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 >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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