From: "Ted Ts'o" <tytso@mit.edu>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg KH <greg@kroah.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: printk() vs tty_io
Date: Wed, 14 Dec 2011 09:05:27 -0500 [thread overview]
Message-ID: <20111214140527.GA18080@thunk.org> (raw)
In-Reply-To: <1323860206.28489.35.camel@twins>
On Wed, Dec 14, 2011 at 11:56:46AM +0100, Peter Zijlstra wrote:
>
> Well, this was the 8250 serial port driver doing wakeups. Its a simple
> on-board serial port,
>
> [ 29.797007] [<ffffffff8108a650>] __wake_up_common+0x4e/0x84
> [ 29.797007] [<ffffffff8108d6ea>] __wake_up+0x39/0x4d
> [ 29.797007] [<ffffffff8135d0db>] tty_wakeup+0x5b/0x60
> [ 29.797007] [<ffffffff81373fb9>] uart_write_wakeup+0x21/0x23
> [ 29.797007] [<ffffffff81376899>] transmit_chars+0xd8/0x12f
> [ 29.797007] [<ffffffff81377f3a>] serial8250_handle_port+0x2d9/0x2fd
> [ 29.797007] [<ffffffff81377fcb>] serial8250_handle_irq+0x16/0x1d
> [ 29.797007] [<ffffffff81377ff5>] serial8250_default_handle_irq+0x23/0x27
> [ 29.797007] [<ffffffff81377ade>] serial8250_interrupt+0x4d/0xc6
> [ 29.797007] [<ffffffff810c9ae8>] handle_irq_event_percpu+0xab/0x1fc
> [ 29.797007] [<ffffffff810c9c7a>] handle_irq_event+0x41/0x61
> [ 29.797007] [<ffffffff810cc4cd>] handle_edge_irq+0xd1/0xf6
> [ 29.797007] [<ffffffff8103ab85>] handle_irq+0x24/0x2f
> [ 29.797007] [<ffffffff8150acdd>] do_IRQ+0x4d/0xb3
>
> which places the wakeup under uport->lock, serial8250_console_write()
> takes uport->lock, under console_sem, connecting the locks.
printk() goes through serial8250_console_write() which writes to the
UART device using a busy loop, with local IRQ's disabled. So it's not
serial8250_console_write() which is waking things up; this is coming
form interrupt handler running on some different CPU.
Am I missing something?
- Ted
next prev parent reply other threads:[~2011-12-14 14:05 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-13 19:33 printk() vs tty_io Peter Zijlstra
2011-12-13 23:52 ` Linus Torvalds
2011-12-14 9:38 ` Peter Zijlstra
2011-12-14 10:43 ` Alan Cox
2011-12-14 10:56 ` Peter Zijlstra
2011-12-14 14:05 ` Ted Ts'o [this message]
2011-12-14 14:23 ` Peter Zijlstra
2011-12-14 15:54 ` Linus Torvalds
2011-12-15 9:56 ` Peter Zijlstra
2011-12-15 10:32 ` Alan Cox
2011-12-15 10:55 ` Peter Zijlstra
2011-12-15 17:08 ` Linus Torvalds
2011-12-15 18:07 ` Ingo Molnar
2011-12-15 21:22 ` Alan Cox
2011-12-16 13:25 ` Peter Zijlstra
2011-12-15 19:02 ` Greg KH
2011-12-14 6:59 ` Ingo Molnar
2011-12-14 9:40 ` [PATCH] arch, early_printk: Consolidate early_printk() implementations Peter Zijlstra
2011-12-14 9:41 ` [PATCH] lockdep: Enable earlyprintk output Peter Zijlstra
2011-12-14 9:43 ` printk() vs tty_io Peter Zijlstra
2011-12-14 9:46 ` Ingo Molnar
2011-12-21 12:03 ` Stijn Devriendt
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